I worked as a cleaner for Interserve for 6 years at HMRC in Washington, Tyne & Wear, before the contract was taken over by another company.
We had a good cleaning team that worked well together. Pay was always correct and on time. Management is luck of the draw I think. We started out with a manager so laid back that it was hard to get problems sorted - more... quickly such as when equipment needed replacing. After they left, the new manager was excellent - very proactive and made sure problems were sorted promptly.
As with many such companies I think worker experience will vary from site to site. - less