Unfortunately there can (and will) be service charges. All freehold means really is that you have (along with the other flat owners in the block) control over the building and can obtain your own quotes for buildings insurance for example.
People that later acquire the freehold use the opportunity to extend the leases of the flats to 999 years to become a "virtual" freehold, but you still have to pay towards shared costs for the building.
I'm just about to go to a meeting of a block of 200 flats that has a share of a freehold, but they still have to pay the communal services like lift maintenance and concierge staff.
My old flat didn't have service charges, but that was because we didn't have any common parts at all.
We also didn't have a sinking fund for any major repairs that might need doing to the roof, so we'd have just had to pay for our 1/4th share if that ever happened (which it never did, thankfully!)
I suspect the £1,100 is made up of buildings insurance and reserves for future long term maintenance costs like the roof. Depending on how the property is set up, it might also include water rates and probably electricity for any shared parts (maybe a light in the front hallway?!).