London property buying agent

I need an experienced and well connected London-based buying agent to help me through the process of searching, finding and buying a property in London (£400-450k budget). Ideally covering:
- advice on best areas for my requirements and budget
- searching ads, contacting agents, organising viewings, even accompanying me for viewings
- research on property prices, negotiation on my behalf
- connection with solicitor, surveyor etc until the keys are in my hand.
I put a placeholder budget, but amount will be conmensurate with level of service that can be provided and demonstrable experience and past success.