I have this problem has well, and as i am a first time buyer i can't afford to have the concrete guttering replaced, but i was thinking i could fiberglass it all the away across and then floatcoat it (gel) do you think this would work?
NO
Fibreglass is a brittle, hard, non-elastomeric product. It is useless to line a finlock gutter. Within 5 years it will split, crack or come away from the concrete, water will get in behind, and your problems will be worse than before - wasting your money.
My advice would be as follows
1) Removal - Removal is a very skilled, lengthy and thus expensive job IF DONE PROPERLY. There are a lot of cowboys out there (I am sure no poster on this forum is included in that of course) who just hack off the gutter and fit fascias and a new uPVC gutter in it's place. Some of the work I've seen is appalling, and at least one company has been on Watchdog. If you are shopping around for the cheapest quote to remove the finlock, you are going to seriously come unstuck, because cheapest is NOT the way to go here! Only use someone for this kind of work who's highly reputable - and ideally members of Trading Standards Buy With Confidence scheme or the Which? Trusted Traders scheme.
2) Lining. As mentioned here elsewhere, you can get a plygene lining. This should work (not if the problem is condensation but if it's a leak) but again must be carried out by an expert.
3) A proper, FULLY elastomeric seamless liner. Ideally on a semi, you AND your neighbour(s) should always have the work done together, otherwise no matter what you do there will always be a join, or edge somewhere. If you use an "off the shelf" product, be prepared to re-do / check annually - there are products available that should last 30-50 years + but they tend to only be sold to professional installers.
Whatever you do don't buy on price with this job, buy on a company that CAN do what they say, not one who CLAIMS to do what they say.