Never even consider becoming IMC without an IMC or IR rating.
If there is no other way tell Gatwick that you need an urgent weather diversion to avoid becoming IMC. There is no need to declare a pan unless they refuse which is very very unlikely. Tell them what you need - request immediate right turn 40 degrees on to heading x and immediate clearance into CAS.
You will get it every time.
Better still before you ever get into that situation go do an IMC rating - even if the clowns do away with it you will be qualified to enter cloud in an emergency even if not legal!