Welcome from Oxfordshire !
I buy my parts either from
https://www.autodoc.co.uk/ - Cheap but good brands, takes 5-8 days to arrive, I would recommend Gates for this hose
or
https://www.sytnerstevenagebmwparts.co.uk/ - Genuine BMW parts, postage is about £8 for me, more expensive, better quality
However, I am not using my car yet so don't mind long wait times, if you need it fast maybe try amazon or eBay
For all these sites, make sure the part numbers match !!
Chris.