This is a tricky one due to lack of detail on how the risk register has been incorporated into the Prices.
Firstly, all references in the contract talk about the Prices and do not use the wording in the Contract Data Part 2 i.e. the "TENDERED total of the Prices is £_____ . __", so my view is that it is what is in the activity schedule that counts, not what is stated under this entry.
You then have to look at the how the risk register has been incorporated into the lump sum tender, which you give no details of so I can't really comment on.
Then you have to look at how risks have been priced and whether dealing with them could be considered 'an activity' as the Contractor is only pad for completed activities.
So there are a lot of 'what-ifs' to know before I could give you any sort of definitive answer.