Cheapest place to get them in the UK would be - the US!
Even if you get stung for customs / postal charges, you will typically only end up paying 60%-70% of UK retail price. You are very unlikely to find a UK retailer selling Leatherman gear in the UK below RRP, as the UK sole importer do not permit it.
It is often worth buying two of the tool you want to get better value for money with shipping, then by trading / selling the second one (still way under UK RRP, so pretty easy to do - everyone's a winner), you can subsidise the cost of the one you keep!
That's how to get (almost) US prices in the UK. I would recommend
www.eleatherman.com, who is a banner member on this site, and felinevet can get Leatherman too I believe.
There is
absolutely nothing illegal in doing this, despite what the importer might say. I have tested this