With a screenplay by regular Carry On scribe Talbot Rothwell, the film is credited as "from an original idea by William Shakespeare".

Numerous sets and costumes from 1963's 20th Century Fox epic Cleopatra, starring Elizabeth Taylor and Richard Burton, were re-used for Cleo. Sid James can be seen dressed in entire costumes originally worn by Burton, whilst Amanda Barrie wore numerous items of Taylor's costumes, including elaborate head-dresses.

Aside from the film itself being somewhat of a spoof of Cleopatra, original poster and publicity artwork for Carry On Cleo copied those of the earlier movie - and Fox successfully brought a copyright infringement case against Cleo's distributor, Anglo Amalgamated, over one particular design based on a painting by Howard Terpning for which they owned the copyright.

The stunt performer who took Barrie's place to roll out of the carpet suffered a broken nose when the rigged table collapsed in a slightly unexpected fashion. Amanda Barrie herself had originally been planned to perform the scene.

Much of the internal scenery used in Cleo had originally been produced for a West End production of Caligulia. Victor Maddern had been in the play, and at the end of the run asked the producer what would happen to the sets. The producer explained that after having spent £40,000 making them, they'd been sold - but all he could get was £150! Maddern offered an extra fiver, and no sooner had taken possession of the scenery than heard about Cleo. He made £800 profit immediately by loaning the scenery to Rogers for the production.

Kenneth Williams' line "Infamy, infamy! They've all got it in for me!" is often quoted as one of the greatest in all 31 Carry On films. However, writer Talbot Rothwell lifted the line - with full consent - from an early script of radio show Take It From Here, by Frank Muir and Denis Norden.

At the time of Cleo's production, Kenneth Connor was starring alongside Frankie Howerd in A Funny Thing Happened On The Way To The Forum on the London stage. The success of the comedy play would ultimately lead to Talbot Rothwell writing the hit comedy series Up Pompeii! for the star - with more than a few ideas eventually lifted from his Cleo screenplay.

As well as the legal woes with 20th Century Fox, Peter Rogers was nearly sued by high street chain Marks & Spencer. They weren't bothered that 'Marcus et Spencius' were slave traders, but that the traders' sign employed their signature gold and green colour scheme. The matter was eventually settled with Rogers agreeing to pen a formal letter of apology.