MoneySavingExpert.com is today warning O2 mobile users to beware making calls to financial service firms, or revealing any other private details, as you could be overheard due to a crossed lines glitch.

We've received a significant number of complaints about this blunder, where one person has been connected to an ongoing conversation in error. They can listen to the call, but can't be heard.

The real danger is many will have no idea they are being overheard. The complaints we've had are only from those who have overheard other people's conversations.

When this story was first published at 2pm, O2 said it was aware of the issue and engineers had been "working on it", but released no further details.

At 2.40pm it called to say the problem had been fixed at 6.15pm last night. But we've heard reports of problems since then.

O2 glitch hits Birmingham and beyond

O2 claims the blunder only affects those in the "Birmingham area". But we've heard reports of people many miles from the Midlands being hit, such as one man in Liverpool who was calling someone else in Liverpool.

MoneySavingExpert.com creator Martin Lewis says: "While on the surface this may seem a minor inconvenience, there is a risk of having your private or financial information overheard and suffering a loss on the back of it.

"Until O2 sorts itself out, the sensible precaution would be to think carefully what you say if you're speaking to someone via the O2 mobile phone network.

"If I were to boil this down, don't be too afraid to use the phone but best to avoid banking and bonking conversations."

Has this happened to you? If so, let us know in the forum discussion. Please let us know when, where you and the person you were calling are based, and which networks you're on.

'Crossover calls'

Here are some examples of complaints we have heard via Twitter.

Nav says: "I heard a man asking when would his cheque clear, last night (Tuesday), 10pm."

Mark Lycett says: "It's not just Birmingham. I live in Liverpool, and I called my bro, also in Liverpool, and we both heard a conversation."

Jo Baxter says: "I'm in Cambridgeshire, and I had one yesterday, so not just the Midlands."

Darren Wilkinson says: "I have heard three cross-calls now, also concerned people may be hearing mine."

Jeni Cantle says: "I'm getting a lot of crossover calls. I was on the phone to my partner on Monday when I was added to a completely different conversation."

Emma Munbodh, who works at MoneySavingExpert.com, experienced many cross-calls on Sunday and Monday while at home in Surrey.

Emma isn't an O2 customer, but her boyfriend, who lives in Worcester, is. On answering his calls, Emma says she couldn't hear him, but instead heard someone else. When she said "hello", she realised she couldn't be heard.

We've heard reports of some people on other networks experiencing similar problems, although it's unclear whether these users were on the phone to an O2 customer.

EE, Vodafone and Three Mobile say they're not experiencing any problems.

O2 has suffered a number of network problems over the past year. In July, hundreds of thousands of customers couldn't use their phone for 24 hours after a glitch.