EE was allowed to re-purpose its 1800 MHz spectrum so that it could launch its 4G services ahead of the 4G auction and now it seems parts of the 900, 1800 and 2100 MHz bands may be used by Vodafone and three for the same purpose.
Ofcom is now consulting on whether providers should be allowed to run 4G on parts of the spectrum they already own, with the consultation ending on 29th March 2013.
O2 and Vodafone has also requested that it be allowed to increase maximum permitted power for its base stations by 3dB (decibels) on their 900 MHz spectrum for 3G. Which would increase the range of these towers and possibly fill in some of the slow-spots that exist across the UK.
Whether re-using spectrum for 4G will have an impact on 3G users is unknown, as it will all depend on the mobile operators and how they operate the network, it may be that the intention is to only re-use the spectrum once 4G handsets are very popular and data use on 3G networks is decreasing in parts of the UK.