Many thanks to the "UNLOCK" team for the service they provided. I tried the code they sent to me but, at first, it didn't work. This was my fault because I tried the 1111, 1234 etc guesses before contacting them. This meant that I had "time locked" the phone. But I followed their excellent instructions, waited 24 hours, tried it again and it is now opened.

I would recommend/use them again.