There was a lot of variation, depending on the local justices who ruled on such matters until the 2003 Act.
A quote from Hansard:
LIQUOR TRAFFIC (HOURS OF SALE).
HC Deb 17 May 1922 vol 154 c395W 395W
Mr. O'CONNOR
asked the Home Secretary whether his attention has been drawn to the state of affairs existing under the Licensing Act of 1921, owing to the licensing justices of different boroughs being permitted to nominate independent hours for the opening and closing of hotels, restaurants and public-houses; whether he is aware that on the north side of Oxford Street these houses open at 5 p.m. and close at 10 p.m., while on the south side they open at 6 p.m. and close at 11 p.m.; and whether, since such legislation practically concedes at least two hours longer for the consumption of alcohol than was intended by the Licensing Act, namely, one hour at the time of commencement on the north side of Oxford Street and one hour additional time at the closing hours on the south side, he will take steps to remove such anomalies?
ยง Mr. SHORTT
I have no power to take any action in this matter.
A look through a 70s GBG will reveal a variety of hours, especially for the morning session, with many especially rural areas opening as early as 10AM. I cant find a copy of the 1921 Act to check but I suspect that most of the flexibility in the 1964 Act was carried forward from before. The big change was the 10pm "terminal hour" out of town.
As I said, if you are writing a book a bit of proper research in the locality you portray get a definitive answer.