Hi Andrea!
I searched high and low for a UK supplier of the High Step. I eventually found a company who advised me that any "new" product which has been produced in the US normally takes at least 18 months to transfer to the UK market. Something to do with there being a "test" period in case anything goes wrong with it. Most UK companies would have to return any defective High Steps back to the US which makes them wary of purchasing until the product has been tried and tested.
I ended up ordering from Fitness Wholesale Online. If you go to Cathe's Home Page and follow the Buyers Link for Steps, etc, there is a link there to the website (sorry, I meant to post the link here but have completely forgotten the website address

!!).
I have just had a quick look on their website and they have the Blue Platform plus 4 risers for $55.45 US (approx £32). If you email them with your address details, they will email you back with a shipping quote (from memory, I think the shipping was approx $20-$25 US or approx £11-14, but don't quote me on this. On top of this I had to pay about £20.00 Duty Tax when it came through our Customs, so it does work out quite expensive. You are probably looking somewhere in the region of £65-£70 total. If you are anything like me, I just had to have it, Lol

!! Of course, if you already have one of the Original Steps then you wouldn't need to order all the risers.
I hope this helps. I know there were other people here from the UK who also bought the High Step from the US, so hopefully they will let you know where they got theirs from and how much it cost, etc.
Let us know how you get on!
Kaz
PS - The High Step package that I mentioned above also comes with one of Cathe's videos at no extra cost (it was "Muscle Endurance" when I bought my step - not sure if it is still the same video now, tho!).