According to the BBFC website (the best reference in this matter...), FRANKENSTEIN and BRIDE OF FRANKENSTEIN were both released by Universal Pictures in UK.
The first one was submitted on Dec. 24, 1931. It was cut to 66'45'' and got a "A" certificate.
"Bride" was submitted on May 17, 1935. It got a "A" certificate, left uncut at 75'16"". It only got a "H" for its re-release in 1943.
"Son" was submitted, not by Universal, but by a company named "RB/JCK" (???) on Jan. 1931, left uncut at 95'39"" and got a "H".

Strangely, if "Son" was considered as "uncut" at 95mns, it shows (apparently) that the version originally released was shorter than the laserdisc and DVD versions now available, both closing at some 99mns if memory is good...