I've only ever used Plumb Center twice.
First time I wanted something around £6. Wouldn't take plastic under £10.
Cash not a problem, but the accounts are much easier using plastic - and everybody else e.g. Wickes. B&Q, Homebase will take plastic for any amount.
Second visit for a bog standard (no pun intended) cistern siphon. £14 + !!!
B& Q rip off price £9:50, Wickes reasonable price £8:99, Screwfix bargain price £4.
Last time I use Plumb Center.