F H Brundle still taking orders and delivering as far as I know.
It's an economy of scale, Brundles can afford to sell it that cheap because they're expecting most customers to buy hundreds of kg of steel at a time and will deliver in their own lorrys, places like Metals4U are for hobbyists who only need a meter or so of a several smaller sections and they'll package and post it using normal couriers. If you go on Parker and add 50 lengths to your basket, the price per length will get halved.I like to keep up to date on who is best, so prompted by the question, I did do a quick price check on various suppliers.
I compared the price of a 6m length of 30mmX30mmX3mm mild steel angle iron (grade s275). Prices are ex VAT.
FH Brundle £8.90
Parker Steel £18.43
The Metal Store £21.90
Metals4U £30.66
Aluminium Warehouse £64.76 (Don't list 30mm, so this is for 25mm!)
Barretts don't publish prices.
If anyone spots any mistake in the list or can add others please let me know.
The results speak for themselves!