The deal was/is a GMP deal, (Guaranteed Maximum Price). This is not at all uncommon in the industry as it gives certainty on both sides of the agreement.
The only thing I find a bit odd in all of this, is the "Denise negotiated" bit, as LoR would have bid on the project with knowledge of the contractual terms prior to winning it.
GMP doesn't mean that the price will never increase, it simply means that you will not pay more for the project than what has been laid down during Stage 4, technical design. If a client makes changes after the completion of Stage 4 (we are now in stage 5 - construction), the client is liable for all costs that are incurred due to that change (plus X%). It is a way of ensuring that the contractor strive for efficency and value rather than just cracking on and chucking a bill in at the end. Often, you will also find as part of these contracts that a Contractor is limited to profit return. If LoR sign at £500m GMP, but deliver at £400m, they cant simply claim X% profit, as it will be capped and the rest returned to the client. No idea what their cap will be, but as part of a Sub-co team on a number of projets, we woud aim typically for 3% at pricing and deliver at a max of 6%. (I would expect LoR to be in higher than this as Main Contractor.