EE have 2x60Mhz at 1800MHz, which will dropp to 2x50MHz in September and then 2x45MHz in 2015 when Three gets the spectrum that EE were obliged to sell in return for T-Mobile and Orange being allowed to merge. As Bill Ray says, there is plenty of room for a 2x20MHz wide slot for LTE in there. T-Mobile have also bought 2x35MHz at 2600MHz, so they can put another 2x20MHz slot in there (and then some) too. (I believe 2x20Mhz is presently the maximum slot size for LTE, although it is very flexible below that). EE can also manage a 2x5MHz slot at 800MHz.
Vodafone have bought 2x20MHz at 2600MHz, and I guess they will go for a 2x20MHz slot there, in addition to a 2x10MHz slot at 800MHz. That sounds sensible, too.
O2 on the other hand have nothing at 2600MHz, only about 2x5MHz (or just over that) at 1800MHz, and 2x10MHz at 800MHz. That doesn't seem a lot. They might be able to recycle some of their 900MHz GSM spectrum at some point, but that is not contiguous and at least some of it is needed for 2G, plus there is not a lot of hardware support right now.
Three have that 2x10MHz (that becomes 2x15MHz in 2015) at 1800MHz from September, and also 2x5MHz at 800MHz.
So Three and O2 will not be able to do that wide slot thing that EE are now doing. I wonder if they will suffer because of this, and if so how much they will suffer.
(There's also the possibility that some 2100MHz 3G spectrum might get recycled at some point. The trouble is that it is full of 3G right now, the spectrum bands still aren't all that wide (2x10MHz for O2, 2x15MHz for Vodafone, and 2x20MHz for EE) and "European" variants of phones don't tend to support this band for LTE at present. (Japanese and Korean variants do, however). We may well get rather unequal performance from different networks for reasons of their spectrum holdings.