An Enterprise was bought in in 2000 shortly after the fire to compensate for the rides which were closed. Not sure if it was the same one which was then used for Zodiac from 2001 until it was replaced in 2006.
Detonator is a funny story. The short version: It was bought by the park and installed in the 2001 season too, but the park only applied for temporary planning permission (1 year). It ended up being really popular though, and the park decided to keep it and got permanent permission
The long version, for those interested: After the fire in 2000, Thorpe wanted to use the space affected to get a coaster to open in 2001. Their choices were either a Vekoma SLC, or a Rock n Roller Coaster clone, both of which could have been ready by summer 2001. Plans were actually submitted and approved (I can't remember for which one though), but the park then encountered some issues and ultimately had to shelf the project.
The project was shelved around October 2000, but the park still wanted something in that location (and by that point, plans for Vortex and Zodiac were well under way). A drop tower had been discussed in the past (for the Lost City area), so that's what they went for. Quick and easy to buy and build, easy to get approval, but always intended to be a quick fix until the park put a coaster on that site. That's why they applied for it to only be there a year.
2001 came and it ended up being one of the most popular rides on park. It was unexpectedly popular, and the park felt that had to keep it. They applied for permission again, but only for another temporary term, this time 5 years. The logic there was that because it is effectively a fairground ride that they rushed in, they weren't sure how popular it would be long term, or how it would fair from a maintenance perspective. 5 years passed and they realised it was fine on all fronts, so they sought, and got, permanent permission.
(Let's just take a second to pause here, and be very very grateful for the fact we have Nemesis Inferno over a Vekoma SLC)
Fair to say that it is, seemingly, a different story to Towers' situation.
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As for Towers getting fairground rides temporarily... Yeah, they need flat rides, and that's been a glaring problem for years now. If they only way they can get them is to bring in temporary additions to show there's demand for them, it speaks volumes about the situation the park, and Merlin, are in high up...