As this is a non-residential property they can, in fact, be removed (by force if necessary) immediately. But the police are unlikely to act until the landlord makes a complaint.
The rules on squatters (which is not a legal term, the correct one being trespassers) was substantially updated in 2001 as part of the Civil Procedures Act.
If it were a residential property then an Interim Possession Order would need to be applied for via the court. As soon as an IPO is granted the trespassers have 24 hours to vacate the premises, after which they can be removed by force.
I've never heard of owners being able to use force to remove trespassers in non-residential buildings (or any buildings or land for that matter). Usually owners go through the local court or the high court and don't bother with the IPO. Who would the owners get to apply the force anyway?
The only cases i know of where force was used (contrary to Section 6 of the 1977 Criminal Law Act) are when heavies come round and people then don't usually argue the fine points of the law. But it doesn't happen as much as you would think, thank goodness.