I had 2 identical 'Buy Bitcoin' offers open, 0.6-1.0 bitcoins at a rate of 950GBP
One of them has been accepted, but now both have disappeared. There is nothing in 'My open offers' and the deposit has not been returned
That seems like a bug. It was probably the same offer displayed 2 times. So the security deposit is locked up in the trade. You can check your transactions to see if all is as expected. Also you can use the emergency wallet tool to cross-check the wallet balance. The balance there need to match the balance of available + reserved funds. If not PM me.