Ah so it's down to our lovely government, rather than MAC trying to pull a fast one on us. Don't suppose there's any US-based stores that ship to the UK?
It's tax + customs AND a healthy mark-up. The former typically add 25% to the cost of a knife ordered from overseas (although this is often a crap shoot). £96 for that MAC is taking the pi$$.
That's a crazy price for a MAC knife!
In russian knives stores prices are usually 2-3x times of what they cost in US, but at least we are able to order from US and don't pay any customs or tax fees.