Thanks for all the feedback but @FoamyBanana is right:
You don't need a lawyer to arrange a LPA. They are DIY document available on the government website here:
www.gov.uk/power-of-attorney
You fill the form in and print it off, pay the fee (£82.00 per LPA) then sign it and get your attorneys to sign it and get it witnessed by someone independent (neighbour, friend) then certified by someone (not a family member) who has known you for over 2 years to confirm it is your own decision.
Then you send it to the Office of the Public Guardian.
Many people believe, wrongly, that they need a solicitor to arrange a LPA, and they are often charged hundreds of pounds for the service.
There are also intermediate companies that offer this as a service, at unnecessary additional cost. (A friend who took equity release was encouraged at the same time to arrange LPAs - they sorted it all at an overall cost of over £1,500).
It is a (perfectly understandable) choice to use a solicitor, but it is not a requirement.
It was my mistake to ask a busy GP to certify the document - I misunderstood the instructions, or they weren't initially clear to me, and I was reeling from the shock of a terminal diagnosis so not thinking clearly.
Only later did I realise I could have asked a friend. So the total cost would have been £82.00 per LPA (there are 2, one for health and welfare, one for property and financial) so the most anyone needs to pay to arrange a LPA is £82.00.
I hope this info helps someone in the future, possibly at a vulnerable time.