A double socket is usually rated to 20 amps.

Do you know if it is a ring main with 2
lots of 2.5mm2 or a single 2.5mm2 or a single 4.0mm2 cable?

If it's a ring main, you can use up to a 32A MCB but clearly no point if it's one double and a spur for boiler. So a 20A MCB would be sufficient.

If it's 4.0mm2 then a 20A MCB is also ok.

If it's a single run of 2.5mm2 then you will need to check how it's been clipped.between the consumer unit and the double socket.

Depending on what it's been mounted onto and what surrounds it to determine if it's a 16A or 20A MCB.