Maybe look at shipping from the US ?
Various online stores have had coupons that have been used for Filson items and some will ship to the UK. Likely cheaper than sourcing from within the EU,
A recent example - Brooks Brothers sell the 257 for $300 and they recently had a 25% coupon that could be used on the 257 which would bring it down to $225. According to their site Brooks Bros. will ship to the UK for GBP 5. So, if I am reading everything correctly, you would be looking at approx $235 shipped. Not sure if you would be open to getting hit by any additional import duty/taxes, despite the Brooks Bros. site indicating that they are included in the GBP5.