Sounds like you got caught by east coast Haar.
Sounds like you did completly the right thing and well done for posting letting others learn from your experence.
As note its always worth while giving your destination airport a ring up in jockland. Most have local wx conditions which the locals know about but unfortunatly the met office dosn't seem to pick up on. The haar is famous for sitting off shore for hours then when the tide changes it comes belting in sometimes fast enough to catch people in the circuit. Also because of the nature of the beast it can remove alot of alternates at once ie all the east coast airfields down to nearly Newcastle. And when it does come in it dosn't matter if you have a IMC or IR the RVR's will be that low that fully kitted airliners will be struggling to get in.
Don't let it put you off though. Just have a route backup. If the east coast is looking dodgy the west is usually clear prestwick is always a good bet as a get out.
The subject of decending over water must admit i have done this. But its pretty dodgy even if you know the area and have all the kit and there are some oil rigs at nearly 500ft. And if you have been caught by the haar it ain't going to do you any good at all.
Best thing is a call to D&D and let them do the hard work while you keep the machine safe.
MJ