Plumbing woes

So I thought I'd share my plumbing woes. Bathroom sink was blocked, easy enough to unblock by removing the water trap, job done. Sadly the whole trap assembly was unscrewed and the rubber seals lost. No problem Screwfix is just down the road I'll order a whole new trap as they are cheap, in stock and I can't find the rubber seals on their own. OMG - it turns out the bathroom sink is not a sink - it's a basin. As it's a basin it uses BSP fittings not metric. The waste pipe is metric not BSP. Screwfix don't list the BSP size (the basin connection) they only list the waste size (mm). Thankfully the Screwfix staff are understanding and have told me to just buy them all and return what doesn't fit!
Why can't they simply list the sink/basin connection size followed by the waste/outlet size?
Reading the comments on their site it appears I am not alone. Turns out I need a 1 1/4BSP to 34mm trap - try finding one of those on the Screwfix website!
/rant over