Porting your existing UK number to NumberGroup: timelines, forms and what can go wrong

UK number portability is a legal right under Ofcom General Conditions C7. You own your number; any UK carrier has to port it for you if you ask. In practice, it's a process with a handful of forms, two suppliers coordinating, and a cut-over window. Done well, it's smooth. Done badly, you lose the number on your van.

This is the practical walkthrough — the LOA (Letter of Authority), realistic timelines, what to pre-audit, what can go wrong, and how Ofcom protects you.

What you can port

• UK geographic numbers — 01 and 02 area codes (London 020, all 01xx/01xxx ranges)
• UK-wide non-geographic — 03 ranges (030/033/034/037)
• Freephone — 0800 and 0808
• Business rate — 0843/4/5, 0870/1/2 (though we'd nudge you to port to 03 or 0800 at the same time — those prefixes have consumer-perception baggage)

What we don't port: mobile numbers (07x) — that's a separate process best handled by a mobile-network provider. And 09x premium-rate (those stay with the original premium operator), 070 personal numbers (rarely worth saving), and any number not actually allocated to you (you can't port someone else's number).

The LOA — Letter of Authority

The LOA is the single document that drives the whole port. It's your written instruction to your existing provider to release the number to NumberGroup. We provide the form; you fill it in.

What goes on an LOA

• Account name with the losing provider — must match exactly
• Account number / line reference
• Billing address — match the address on the bill, not your registered office
• List of numbers to be ported (single, range, or whole DDI block)
• Authoriser's name and signature — must be a person authorised to act on the account
• Authoriser's job title
• Date

The single biggest pitfall

Account name on the LOA must match the account name on the bill exactly. Trading-name mismatches cause 85%+ of port rejections. If your bill says "Datazero Ltd" and the LOA says "NumberGroup", the losing provider rejects, and you wait another 7 days for re-submission. Take a copy of the most recent bill and copy the account name letter-for-letter.

Pre-port audit (do this before submitting)

• Inventory every number you own with the losing provider — main number, DDIs, fax line, alarm line, lift autodialler, EPOS, anything that quietly dials out. See our PSTN switch-off guide for the full list of often-forgotten non-voice equipment.
• Check your contract— note the minimum term, notice period, and any "cease" charges. Port-out is free under GC C7 but the underlying line contract isn't cancelled by the port itself.
• Confirm there are no unpaid balances with the losing provider. Outstanding amounts in dispute give them grounds to delay (though not refuse) the port.
• Decide your cut-over window. Avoid peak trading periods, Christmas / Easter / Bank Holidays, or major sales events. A Tuesday or Wednesday morning at 9am is the sweet spot.
• Have the receiving system ready. PBX configured, SIP trunk live, test routes set up — so you can flip in seconds when the port completes.

Realistic timelines

• Single UK geographic (01/02): 5–10 working days from valid LOA to live
• Single UK-wide (03) or freephone (0800/0808): 5–10 working days
• ISDN30 with a sprawling DDI block: 10–15 working days. Larger blocks (100+ DDIs) sometimes longer
• Already-ported numbers (chain ports): 15–20 working days. Each previous port in the chain adds complexity
• Contested or disputed accounts: open-ended. Resolve the underlying dispute first.

Add 1–2 days to all of these between October and December (port queues lengthen as businesses migrate before Christmas).

The process, step by step

Day 0: you submit

• In the portal, go to Numbers → Port In → New Request
• Fill in the LOA on screen, or upload a signed PDF
• List the numbers
• Pick a target cut-over date (at least 7 working days out for geographic, 10 for ISDN30)

Days 1–2: we validate and lodge

We check the LOA for the common pitfalls (matching names, right numbers, signatory authorised) and lodge it with the losing provider via the standard wholesale porting interface.

Days 3–7: losing provider validates

Their porting team validates the LOA against their billing records. If they accept, they confirm the cut-over date back to us. If they reject, they tell us why — usually a name mismatch — and we re-submit.

Days 7–10 (geographic) or 10–15 (ISDN30): cut-over

At the agreed cut-over time, the number routes to our network instead of theirs. Callers hear no difference. Your PBX or handset starts ringing on the new system the moment the cut-over completes.

Day after: tidy up

• Confirm every ported number rings
• Confirm outbound dials present the right CLI
• Update Google Business Profile, your website footer, and any printed materials with whatever's changed (usually nothing — the number is the same)
• Now send the termination notice to the losing provider

What can go wrong

The losing provider rejects the port

Usually a mismatched account name. We'll tell you what they said and you re-submit. Adds 3–7 days.

The losing provider delays the cut-over

Most common reason: an unpaid balance you didn't know about. Settle and the port proceeds. We'll escalate through the wholesale interface if delays are unreasonable — GC C7 gives the receiving carrier (us) the right to escalate to Ofcom for genuinely bad behaviour.

Numbers ported but old contract still billing

Port and contract are legally independent. If you forget to terminate, the old provider keeps billing you for the line service (not the number — they no longer have it). Read your contract's notice clause carefully and schedule the termination.

Your number sits behind a reseller chain

This is the big one most guides skip. The company you pay isn't always the company that holds the number. Plenty of UK telecoms are resellers buying from a wholesaler, who in turn buys from the actual range-holder. Your number might be three or four links down that chain. Every link has to action the port in turn, and each one can add days — a clean single port that should take 5–10 working days can stretch to 3–4 weeks purely because the request has to walk back up the supply chain. There's nothing illegal about it and we can't force a downstream provider to move faster than their process — but because we're a carrier with direct wholesale access, we lodge through the right interface and chase every link rather than leaving you to. You won't always know your number is behind a chain until the losing provider responds; we'll tell you the moment we find out so the timeline is never a surprise.

Hidden non-voice equipment stops working

Your fax / alarm dialler / lift phone was on a line that ported. Sometimes the line itself ports with the number; sometimes only the number ports and the line ceases. Pre-port audit prevents this. Common in older ISDN30 migrations.

You needed the number to stop ringing temporarily

Port windows are non-trivial to push back once agreed — give us 24–48h notice if you need to delay. Last-minute changes are possible but you may slip a week.

How Ofcom protects you

• GC C7.1 — UK numbers are portable to any UK carrier
• GC C7.4 — losing provider can't charge a port-out fee on top of normal usage charges
• GC C7.6 — the cut-over itself is fast once everyone's agreed; the time is spent on validation and (where it applies) walking the request through a reseller supply chain, not the switch-over. Don't read "one working day" as "ported overnight" — the days are in getting to the cut-over, not the cut-over.
• Ofcom enforcement — for systematic obstruction, complaints go to Ofcom directly. They have fined providers for delaying ports.

Doing this with NumberGroup Membership

• Port-in is free with Membership
• We handle the LOA validation, lodging and chasing on your behalf
• The receiving end (us) is configured before you port — so there's never a window where the number isn't reachable
• Our UK team coordinates the cut-over window with you — no "at some point between 9am and 5pm" nonsense