What you have here are 7 volumes, with 4 films in each set.
These are all the new Special Edition versions.
Looks like Play.com have numbered 3 of the sets with the same numbers, so volume 1, 2 & 3 are listed twice, but have different films.
Carry On: Vol.1 (Sergeant / Teacher / Nurse / Constable) (4 Discs) - £7.99.
Carry On: Vol.2 (Regardless / Cruising / Jack / Cabby) (4 Discs) - £7.99.
Carry On: Vol.3 (Spying / Cleo / Screaming / Cowboy) (4 Discs) - £7.99.
Carry On: Vol.1 (Up The Khyber / Doctor / Don't Lose Your Head / Follow That Camel) (4 Discs) - £7.99.
Carry On: Vol.2 (Doctor / Camping / Up The Jungle / Henry) (4 Discs) - £7.99.
Carry On: Vol.3 (Loving / At Your Convenience / Matron / Abroad) (4 Discs) - £7.99.
Carry On: Vol.4 (Girls / Dick / England / Behind) (4 Discs) - £7.99.
7 volumes currently available, but if you do buy them this way it works out to just under £2 a film.
Looks like Carry on Emmannuelle, That's Carry On 1978 Clips show & Carry On Columbus are the only missing ones.
Get all of them for 7 x £7.99 = £55.93.
Use £5 off voucher = £50.93.
4% Quidco = -£2.03
Final price £48.90 for 28 Carry On films.
Official Carry On film list:-
Carry On Sergeant 1958 black and white
Carry On Nurse 1959 b&w
Carry On Teacher 1959 b&w
Carry On Constable 1959 b&w
Carry On Regardless 1961 b&w
Carry On Cruising 1962 first colour carry on film
Carry On Cabby 1963 b&w
Carry On Jack 1963 colour
Carry On Spying 1964 b&w
Carry On Cleo 1964 colour, and so were all subsequent films
Carry On Cowboy 1965
Carry On Screaming! 1966
Carry On Don't Lose your Head 1966 Originally released without "carry on" in the title
Carry On Follow that Camel 1967 same as above, "carry on" was added later to both films
Carry On Doctor 1967
Carry On up the Khyber 1968
Carry On Camping 1969
Carry On Again Doctor 1969
Carry On up the Jungle 1970
Carry On Loving 1970
Carry On Henry 1971
Carry On at your Convenience 1971
Carry On Matron 1972
Carry On Abroad 1972
Carry On Girls 1973
Carry On Dick 1974
Carry On Behind 1975
Carry On England 1976
That's Carry On 1978 Clips show
Carry On Emmannuelle 1978 Last of the series
Carry On Columbus 1992 Attempted revival of the film series