Perhaps my time as a moderator on this site has made me over-cynical but I always suspect posts such as this one, coming from a new member, as being the first bit of 'two-part spam'. (i.e. another new member will follow along to praise the services of the company referred to in the question).
Anyway . . .
Quote:
"If you want to come to London, either to join your partner, work, study or just take a holiday and experience the British culture, you will need to obtain a London Visa. The London Visa category is broken down into a number of sub-categories, each with varying requirements, to assess an applicant’s eligibility."
Source:
http://www.immigrationhelplineuk.com/index/uk-london-visa
I certainly wouldn't trust any firm that repeatedly refers to a 'London visa' (as there's no such thing). Further I'd be hesitant about using a company, providing a service where 100% accuracy is required, which can't be bothered to get someone to proof read their own website to get rid of the errors I can easily spot there.
I also wouldn't trust any company that hides behind an 'accommodation address':
http://www.prime-secretarial.co.uk/streetaddress.html
Further, unless a national government has contracted out their visa application process to an accredited agency, I would never consider using any service other than the official one provided by the relevant government as it's a total waste of money.