"[...] Amazon [...]"
There are lots of online component suppliers who have a presence on ebay and the web. They often offer 1st Class RM delivery for free or at a small premium.
For example: Bright Components does 1st Class as standard - and a single fixed P&P of 99p no matter how many things you order. Small components come in reasonable size multiples. Admittedly there are some gaps in the component ranges - but they stock enough things to be useful in a hurry. Typically 250mw carbon resistors of one value - pack of 50 for 99p.