The instruction to stop, or not to start, any work is given by the Project Manager and should be accompanied with details of the reasons why the instruction is given, not least to allow the consequent procedures under the contract to be administered correctly, including the CE procedure under clause 60.1 (4).
The PM should also state assumptions which can be used to price the associated CE quotation, including; length of postponement, measures to be taken during this time to secure the works, retention of 'key resources' etc.
Under clause 91.6 you have the right to notify termination, although only where an instruction to 're-start' any works is not given within 13 weeks. This also only applies to 'substantial' or 'all' work, so may not actually apply.
It looks like you need clarity on the intention, not least to plan how you are going to Provide the Works under these circumstances. I would suggest notifying an early warning to facilitate discussions, not least to make clear what the impact is likely to be on Defined Cost with all the disrupted progress.