Hello
You'll not get a "Visa" unless you have a job - the process to get a work permit is long and tortuous - look to something like six to nine months once you have a job in an in demand profession.
That said you can come an spend your money here for up to 26 weeks by coming as a visitor and applying for extensions (up to the six months), you do have to have a reason to get extensions ("looking for a job" is the one guaranteed to get the application rejected).
There is no such thing as a general work permit - it is specific to the employer and the job.
In demand jobs are those related to medical specialists, quantity surveyors, other construction professions, certain senior hospitality positions, specialist chefs (e.g. asian cuisine).
Those not in demand lawyers (there are hundred and hundreds of locally qualified lawyers), PR, HR, mod level finance.
One last thing - this is an expensive place to live, think Central London overall.
If you like get in touch when you are over and I should be able to connect you to some people who will be able to confirm whether your are wasting your time and effort.