The British deterrent was (and still is) declared to NATO, so they would have had NATO assigned targets in accordance with the SIOP. However, Polaris was capable of unilateral use in the event of a 'supreme national emergency', therefore there would also have been a UK target list as well as SIOP ones. Hitting Moscow was seen as key from the start of the V Bomber days.
The problem was that in the late sixties the Soviets put an ABM system around Moscow. The US Navy replaced their Polaris missiles with Poseidon, which had Multiple Independent Re-entry Vehicles, and the missiles fitted in the same SSBNs and same tubes as Polaris. However, the UK was trying to join the Common Market, and Ted Heath did not want to risk upsetting the French and said 'no' to the idea of acquiring Poseidon - yet another American missile. Although Poseidon was a larger missile than Polaris, the Americans found they they could squeeze it in to the missile tubes in existing SSBNs.
Chevaline was technically ambitious, particularly as the UK had given up both long range missile technology and space launcher technology. There was also concern by the RN that the reduced range of the new system limited the area of ocean that the duty bomber could hide in.