I am assuming that you have a UK passport since you said you are British. Are you officially engaged? Do you have a wedding date set? I am not a solicitor, but I imagine that if you were officially engaged it might help your chances.

I would start looking for a job in the UK now. If you have a UK passport you should be eligible to work there. Ask your parents for leads or start an Internet search. It may be harder for your gf to qualify for work there, but depending on her skill set she may be able to find work also. It would seem that if at least one of you was employed that your chances of gaining approval for a visa would be better. In the meantime, you may check the EasyExpat guide for London for possible job leads. The link is here: http://www.easyexpat.com/en/guides/united-kingdom/london/job/adverts-recruitment.htm

That is a question to ask a solicitor. However, EasyExpat has a guide for London where you may be able to find general visa information. The link for visa regulations is here.http://www.easyexpat.com/en/guides/united-kingdom/london/departure/passport-visa.htm

I would ask a solicitor about that to be sure, but if you do put your employment on the application, be sure to indicate that it is outside the UK.

Besides contacting a solicitor, you should consider contacting the British embassy/consulate in Peru. The link is here: http://www.fco.gov.uk/en/travel-and-living-abroad/find-an-embassy/south-america/embassy-lima

Good luck!