For my company i am using NetworkFish IT support services since 3 years.They provide IT support for London’s SMEs with 24hr, SLA-backed IT support services, for on-site, remote IT engineer support and IT helpdesk support services for your staff. They also manage the backup and data flow. They provide a facility where you can calculate your cost for services.
They provide 24/7 suppport services. I suggest you to try there services.
For more information: http://www.networkfish.com
Visit the website https://www.itsupportlondon365.com/
My company has collaborated with them more than once, and it was a good experience.