I file all my negs in clear Print File archival negative preservers. For 35mm, I use the #35-7B, which provides 7 rows for 5 negs per row. The 36th (and sometimes 37th) negatives are just slid beneath the last strip, so a full roll will fit. I number and date each roll. The sheets are punched for a standard 3 ring binder. I use archival binders from Light Impressions; I suppose something similar is available in the UK. I also have Print Files for 120 and 4x5.
When I order prints, I just pull out the strip of negatives from the sheet and place it in a Mylar sleeve. I put all the sleeved negs from one roll into an envelope with the frame numbers, sizes and quantities written on the envelope. Your lab may provide envelopes for this purpose; if not, furnish your own.
When the prints are returned, I number the back of each print with the negative number for identification in case of reorders, then refile the negs in the Print File pages. I have about 32 years' worth of negatives filed this way, and the binders fill a long shelf in my darkroom. The most recent 5 years are filed under my enlarger table for quick access.