Vasco, the RAF was never going to afford the KC10 in the early 1980's. The country was broke. The BA/RAF TriStar deal was manna from heaven, Lady Thatcher was able to boost her favourite business barons and, it was a major element in setting BA on the path to success.
Unfortunately, the RAF senior management was unable to fully capitalise on the capabilities of the TriStar. The wing mounted refuelling pods were perfectly capable of being fitted. However, financial limitations and lobbying by interested parties robbed them (and the money) for the various VC10 rebuilds.
OAP