Alright buddy,
Yeah, the savings are pretty good on certain things actually!
I got this trade card through a membership with
Vauxhall Owners Network - Powered by vBulletin back in the days, had it ever since - It doesnt expire you see, so remains valid forever.

You would need to speak to Halfords, and likely provide letterhead proof of your autmotive business. Pop in store and ask for an application form for trade accounts. In reality, qualifying for it would be very easy, and as you pay as you go, no credit checks or account setups would be needed.
It basically covers are maintenance parts, consumables, oils/fluids and all tools. It doesnt cover ICE, performance parts, or anything that isnt a routine maintenance part.
A few examples of things I've purchased in the last few months are:
Dash Bulbs (the ones you usually replace with leds) 45p each trade, rrp: £1.99 or thereabouts
501 side light bulbs 48p for a pair trade, £2.19 normal price
Halfords assorted o ring set £3.99 trade, £6.49 retail
Battery (advanced HD one for 3.0) £54.99 trade, £79.99 retail
Windscreen wipers like Bosch are almost buy one get one free
Bulbs are stupidly discounted
Haynes manuals are discounted
All tools/tool chests etc are discounted around 20% or more in some cases.
One thing to remember though, is using a trade card you dont get the normal offers. So if screen wash is buy one get one free, your better buying at retail, as trade will only give you like a £1.50 off each one etc.
Its handy to have, saves you a fortune over its lifetime - Especially for things like bulbs, and engine oil/coolant/brake fluid/screenwash/lubricants etc etc.
Your still better off using trade club at Vauxhall for engine oil and service parts though, as thats even more discounted than what you get from your trade card at halfords.