Prices do vary, look here for uk suppliers. These are Canon agents so they have come through Canon UK.
https://www.camerapricebuster.co.uk...s/Canon-EF-100-400mm-f4.5-5.6L-IS-II-USM-Lens
A lot of UK photographers use people importing them from Japan, Grey Imports, and can be a lot cheaper but usually without the Canon UK warranty, but a warranty supplied by the seller, like these who have a uk shop also.
https://www.hdewcameras.co.uk/canon-ef-100-400mm-f45-56l-is-ii-usm-2980-p.asp
£1289 from e-infin.com/uk/ - I'd recommend them too.
Yes, I've purchased twice from them. Both times they were very efficient with excellent communications. It seems to me that once these 'grey' companies get known, their prices start to creep up. The newer companies need to break into the market so tend to be the most competitive.