The Valiant, when first designed, was envisaged with underwing bomb carriers that could take a 10,000 lb bomb or similar. It was never carried through but it enabled a 12,500lb capacity fuel tank to be fitted in its place. The Americans adopted a similar idea that was hung on to the Skybolt carriers on the B52 which enabled them to truck even more explosives to North Vietnam.
What they should have done was.......
When the Valiants were scrapped they should have shipped the underwing tanks to 1 Group and asked A V Roe to make some fairing adapters so that they could be hung from the Vulcan 2's Skybolt fittings.
The Valiant tanks were fully independent with their own pumps, pressurisation and jettison system. A bit of plumbing and electrical work and you had another 25,000lbs fuel capacity.
It would not have been able to take off with this and a full bomb load but topped up after take off it would have made Black Buck a lot easier.