Already before Skybolt's cancellation British Air Ministry (already aware of its development problems and afraid of possible cancellation) drew up in january 1961 OR.1182 for a stand-off weapon for V-bombers to be in service by 1966. It was supposed to have range of 1000nm with Mach 3 speed at high altitude and Mach 2 terrain-following for the last 100nm.
Avro designed W.140, though it didn't quite met the demands (calculations said it would fly Mach 3 at 70000ft - 21336m, but only Mach 1,5 at sea level, while the range was initially just 580nm, during design work improved to 950nm), while Bristol designed X.12 also called Pandora, which was supposed to be capable of Mach 3 at high altitude (with possible Mach 4 after changes to airframe materials) and up to Mach 2,8 at low altitude, though this design in turn suffered from high weight of 15000lbs (6804kg), so even VC.10 or Victor B.2 stage 3 could get no more than 4 of these.
Soon the OR.1182 was dropped, but Bristol designed X.12B that was a three-stage solid rocket version of X.12 to be launched from VC.10, but it met with no official interest, and after the cancellation of Skybolt the British were left without modern deterrent, so a frantic search for options ensued. Most of the proposals seemed to be short range interim ones, except for Bristol Grand Slam (unrelated to WW2 bomb) - first version was a 100nm ranged rocket-propelled toss-bomb to be launched from TSR.2, but it's improvement, Grand Slam II was to be a 50ft (15,2m) long, weight 32000lbs (14515kg) for a range of 1300nm (2408km) at Mach 3 speed for first 500nm, then a low-level Mach 2 for 700nm only to pitch up in the end to toss the Grand Slam onto the target from 100nm.
(there were also proposals for air-launched Polaris and Pershing, but, well...
![Rolling Eyes :roll:](./images/smilies/icon_rolleyes.gif)
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Source: Chris Gibson & Tony Buttler, British Secret Projects. Hypersonics, Ramjets & Missiles, Hersham 2007, p. 114-117.