Laws, the specimen lake at The Riddings is very small. At it's narrowest point you could almost jump across it with a good enough run-up. No bait boat needed, trust me. It's also rather expensive for what it is.
Earlswood Lake/Reservoir may be a better bet. Go on Engine Pool. Dunno if bait boats are allowed but it's certainly large enough to justify the use of one. It's owned and run by British Waterways, maybe their website will offer more information.
Pine Pool at Kingsbury Water Park is their carp specimen pool and is a pleasant place to be. Very clear water so I set up well back from the waters edge and don't have my rod tips hanging over the water. Dunno about bait boats being allowed, sorry.
I haven't fished either of the other venues so can't comment, sorry.
Ian