Is it that much of a shock when you take into account that the £ has dropped over 10% against the €?
All mine were new in March/April, and have about 1000 miles on them - at my current rate they should last 20 years - so plenty of time for the £ to recover
However, on the site I last used, they price for a rear (265/40r18 in my case) has gone from £155 to £185 - so more like a 20% jump. Fronts have only gone up £5/5% though.