SIM Swap Fraud UK: Warning Signs & What to Do
Sudden, unexplained loss of mobile signal is worth checking immediately — even though it's usually nothing.
What SIM swap fraud is
SIM swap fraud is when a criminal takes control of your mobile number without your consent, so they receive your calls and texts instead of you — including one-time security codes. This happens in one of two closely related ways: a criminal convinces your own mobile network to issue a replacement SIM for your number (sometimes called SIM splitting), or a criminal ports your number to a different network on a SIM they control, using the standard number-switching process.
Why it's so effective
Once someone controls your number, they can intercept SMS-based one-time codes and password reset messages for banking, email, and other accounts — the same codes that are supposed to prove it's really you. That's what makes SIM swap fraud valuable to criminals: it doesn't just disrupt your phone, it can unlock other accounts that rely on a text message as a security check.
Signs of a SIM swap attempt or attack
- Your phone suddenly and completely loses signal or service, with no calls or texts going through — a leading warning sign, but check for other signs too, since a delay activating a new SIM or a genuine network fault can look similar.
- You receive an unexpected text about a number port or SIM request you didn't make.
- You get password-reset emails or account-lockout notices you didn't trigger.
- Someone contacts you claiming to be from your mobile network asking for personal or security information out of the blue.
How the scam works step by step
First, a criminal gathers enough personal information about you — through phishing, a data breach, or social engineering — to pass basic identity checks. Second, they either contact your mobile network claiming your phone is lost or damaged to request a replacement SIM, or they request a port of your number to a new network. Third, your phone loses signal as the swap or port completes. Fourth, they use SMS codes sent to your number to attempt to break into your banking, email, or other accounts.
How to protect yourself and spot the signs early
Treat sudden, total loss of signal seriously, but check for corroborating signs — like an unexpected porting text or account lockout notices — rather than assuming the worst from signal loss alone, since normal SIM activation delays or network faults can look identical.
- Where possible, use an authenticator app rather than relying only on text-message codes for your most important accounts.
- Many UK mobile networks now offer an extra account-security step, such as two-factor login on your online account — check your network's app or account settings and turn it on.
If you think you've been SIM-swapped
Contact your mobile network immediately using a different phone, device, or their website/app — not the affected line, since it may no longer work. Check your bank accounts and email for unauthorised access, transactions, or password resets you didn't request, and contact your bank straight away if you see anything unfamiliar.
How to report SIM swap fraud (UK)
Report it to Report Fraud at reportfraud.police.uk or 0300 123 2040 if you are in England, Wales, or Northern Ireland. In Scotland, report to Police Scotland on 101.
Frequently asked questions
Can my mobile network legitimately ask me to verify my identity before a SIM swap?
Yes — providers should verify that a SIM swap or number switch is authorised, but the exact checks vary by network. The best defence is turning on any extra account-security option your network offers yourself, rather than relying on provider checks alone.
Does Ofcom require ID checks before a SIM swap or port?
Ofcom's porting rules require providers to handle number transfers properly, but there is not a single universal ID or PIN check that applies in the same way across every mobile network. Check your own provider's SIM-swap and porting security settings.
My phone suddenly lost signal — does that definitely mean I've been SIM-swapped?
Not necessarily — it can also be a SIM activation delay or a genuine network fault. Treat it seriously, especially alongside other signs like an unexpected porting text, and contact your network via another device to check.
If a scammer accessed my bank account after a SIM swap, can I get my money back?
Contact your bank immediately and report what happened — this is different from a payment you were tricked into authorising yourself, and different protections may apply depending on exactly what occurred. There's no guarantee, but acting fast and reporting it gives you the best chance.
How do I report a SIM swap attempt or fraud in the UK?
Report it to Report Fraud at reportfraud.police.uk or 0300 123 2040 (Police Scotland on 101 in Scotland).