Personally, I would always prefer to have my property managed by an experienced superhost that offers co-hosting services, rather than a management company. You can find them by clicking on the co-host tab at the top of your listing.
If you want to use a management company, there is a London hosts forum on FB I think, so you are probably best asking them for recommendations.
Don’t forget you can only let your place for 90 days a year for a whole listing in London.