Plumbfix (a subsidiary of B&Q / Screwfix) recently opened up a catalogue service and published the number 08081010000 for all purposes, including orders.

As everyone (except perhaps Plumbfix!) knows, this number is CHARGEABLE from any UK mobile.  Plumbfix don't publish any other (national-code) number and didn't even seem to know one when I asked them.
Silly or what?

Screwfix apparently works from the same location and has an 0845 number (0845 414141), for which 01935 414141 works as an alternative but Plumbfix apparently hasn't thought about the problem - yet.

Thanks for the 020 redirecting numbers
BTW, only the first one (020 0222 0700) works from T-Mobile.
The other one gets a funny message asking 'Are you sure you dialled right? If so, it won't connect' or somesuch.

Presumably, the mobile co-s hate these numbers and block them if they can.

Clearly Screwfix knows that there are issues with freephone numbers as it has gone to the trouble of obtaining matching free and local telephone numbers, ie 0500 414141 and 01935 414141. It should be praised for providing a free number for main contact whilst providing an alternative for mobile users.

I suggest you write to them and raise the issue of an alternative for Plumbfix. Details of management are here.

This page on Kingfisher Plc's website (Screwfix's parent company) suggests email addresses are of the form firstname{dot}lastname{at}screwfix{dot}com Perhaps you could email the management and suggest that an alternative be provided for Plumbfix.