Your Class 1 initial medical has to be taken at Gatwick - look on the CAA website for details - after that, any AME with a number beginning with a 1 can do the renewal.
I would recommend you do your Class 1 first before you start studying as that is the toughest one to get through.
You can get Loss of Licence insurance but it is costly as probably wouldn't be worth it if all you stand to lose is the cost of ground school.
Cheers
Whirls