Until we see otherwise, this is unlikely to be related to a major investment, but there is a digger on the old Treasure Island plot:
https://x.com/ThorpeParkMania/status/1878473914944282751
Treasure Island does feature a service road that links the park's main engineering workshop to the park, but this digger is away from that road.
There's a hundred and one potential reasons for it to exist there. But one of those reasons is early work related a future investment...