Vodafone owns 45% of Verizon Wireless. You can bet that they'd be doing the same thing in the UK if the government would let them.
Not regulating which technologies mobile phone companies can use lead to a multitude of incompatible networks (GSM, UMTS, iDEN, CDMA2000) in the US.
It also, however, lead Qualcomm to develop IS-95 (CDMAone). In Europe, that never would have happened, because everyone was required to use GSM.
Guess what? Large portions of UMTS are based on technologies developed by Qualcomm for CDMA.
So, yeah, I guess I'll put up with only having two national GSM/UMTS provider choices (T-Mobile and AT&T).
Regulation always has consequences. Some of them are good (compatibility between networks). Some of them are bad (stifling innovation in new mobile technologies).