Hi there! I am a British FiveM developer, I currently work for a large well known FiveM RP server (can provide proof). Although this server is not British themed, I have developed for it a custom framework, so can develop scripts for you if needed. I work mainly in C# but am well versed in lua, and am sure I can work on making a vRP server British themed. I can not develop cars or peds myself, but if they are available already (which many are), I can put them in the server. I can also setup the server with the interiors. Whatever you find, as long as it is compatible with FiveM, I can install. As I said I can also develop custom scripts if needed.
Looking forward to working with you!