I actually can't find any more where it tells you that the postcode letter has to exactly match the id so I don't know if it's just me or if they have changed it.
It definitely used to be the case though because I specifically changed my husband's name on the utility bill only for that reason.
Either way, I would still definitely make sure that the names all match exactly because there is plenty of anecdotal evidence of people being turned away for not having an exact match and the test centres will be likely to stick to it because that's what they are used to.
From page 7 of the terms and conditions download.
If the following details are not correct on the day of your test, or
not consistent with the ID and postcode evidence provided,
you will not be allowed to take the test and will not receive a
refund of your test fee:
names
date of birth
country you were born in
nationality
place of birth
ID
ID must be in date (unless this is a passport or
an immigration status document)
proof of postcode (this must contain your name and you
must bring this with you to the test).