Does anyone in the UK have a recommendation for a decent sit/stand desk for a reasonable price? IKEA have some lovely ones but they are significantly more expensive than the regular sort of desk (£450 vs. ~£80...).
I believe the IKEA desk you are referring to is the IKEA BEKANT. In the standing desk world, this is one of the cheapest ones out there. I was able to test one out at a local IKEA store and my initial reaction was: this could be pretty cool! The wirecutter has an extensive review of standing desks that you may find helpful if you did not already come across it. You will discover useful information in the comments, too.
http://thewirecutter.com/reviews/best-standing-desk/
If you already have a suitable sitting desk, consider one of these: http://www.varidesk.com/. I lobbied for these at work and now we have hundreds of them, they are universally liked. I have 2 24" monitors on mine and it is very sturdy when in standing mode.