Engine failure and engine shutdown

Hi

Sorry if this is in the wring forum. I have a 1.6 diesel focus estate. It's a 58 plate but registered in 2009. I only brought it in December privately. Yesterday it cut out in my husband but he managed to get it started straight away. As it was very wet, we presumed it was the amount to of water but we said we would keep an eye on it. Today it cut out completely and would not start. I called a garage who said to remove the key, lock the car reopen the car and start the engine again. He did it 3 times and it eventually restarted and he got home with out further issues. I called the garage back who said that it was the key and to use the spare for now. I have done this tonight but when pulling out of the carpark it did it again with the spare key. It too 2 attempts of locking, opening and restarting. When it goes, everything goes and all the lights light up with engine failure message. The car will not start unless you lock and open the car again. Are we looking at a serious fault? Surely this is more than just the key. It is booked in tomorrow afternoon but I am really worried especially as we haven't had it long.

Thank you for reading and help.