You could try ordering the cetificate I mentioned from the GRO (
www.gro.gov.uk) but don't use the reference.
Their site asks if you know the reference or not, it defaults to 'no' so then you enter the year as 1926 and go to the next page.
I've attached a screen shot
Enter his name as Alan Evans and date of birth as per their example 01/01/1926 not the date I posted as that could be wrong, for the place of birth fill in Marylebone, leave the fathers name blank. When you get to the mothers name, leave the surname blank and fill in 'Mother's surname at time of the birth' as Evans. For her forenames enter 'Edith Annie or Edith'.
The GRO should look at the entry in the register and if the mothers name is not Edith Annie or Edith, they'll email you and you'll get your money back.
This service currently takes about 24 days or you could order the cert and have it back in about a week by quoting the reference. However the cert could be wrong and you won't get your money back.