Hi V1-rotate,
I'm very much like yourself.My right failed the intial Class 1 standards.Already holding my PPL they CAA did offer the "deviation" rule/allowance.So I have since been over,and thankfully PASSED my Class 1 with a deviation which like you mentioned will become a full medical once my training is complete.
What happens is youll go to Gatwick like everyone else and will have an "Eyes first" examination.If the optician feels he cannot give you the deviation to the Class 1 then you are only liable for the eye exam rather than the full whack £422!!
I went through this process with seeing the optician a Mr.Chorley.He'll tell you there and then and should he see fit to allow a deviation you then go on to carryout the rest of the medical.
Anything else just ask,Best of luck,was in your shoes so know how it feels
Regards Gavin