The movie clearly states that it is the middle of the summer and supported by the fact that schools are still in attendance and the quote "It's the middle of the summer, its a heat-wave." However during the party scene, it is clearly dark outside but the clock on the wall as Jamie enters the house says 9:00. During British Summertime it would still very much be light at this time.
When Jamie is in the tobacconist's looking at the magazines, there are three copies of "Gay Times" in the long shot, but only two in the closeup.
When Leah is dressed up as Mama Cass, she has yellow tights over her head. Between shots the legs of the tights alternate from behind/in front of her shoulders.
After "rescuing" Leah, Tony goes downstairs barefoot, but the sound of shoes can be heard.
When Jamie is about to steal a copy of "Gay Times", the magazines next to "Gay Times" are "Auto Trader" is wide-shots, but "Playboy" in close-ups.
When Jamie and Ste board the 180 for the Gloucester, it's actually heading AWAY from London and the bar.
The rainbow early in the movie is inaccurately depicted: the red band should be outside the curve, and the blue/violet band on the inside. A rainbow is composed of the entire spectrum of colors of visible light, from the longest wavelength, red, to the shortest wavelength, violet. The order of colors in a rainbow is easiest to remember by the following mnemonic (a formula that helps one remember something): Richard Of York Gave Battle In Vain. R=red, O=orange, Y=yellow, G=green, B=blue, I=indigo, and V=violet. Red is naturally at the top edge (longest, or hottest in the spectrum) of the rainbow and violet is at the bottom edge (shortest, or coolest in the spectrum), with the other colors, in order, in between.
When Ste and Jamie are talking outside at the party, it's cold enough that you can see thin fog from their breath, even though it's supposed to be set during a heatwave. Occasionally, other almost-invisible puffs of fog appear behind Ste (probably from crew members), even though they're supposed to be alone.
When Jamie and his Mum are fighting on the floor of their living room, the transmitter of the body mike is visible on his back underneath his tee-shirt.
Sandra states that she's been offered a pub "in Rotherhithe". However, when she opens the letter that gives the address of the pub, it clearly states Greenwich. Rotherhithe is over 3 miles away from Greenwich. However, when Sandra and Jamie visit the pub ('The Anchor') it is at Ballast Quay in Greenwich.
When Leah is "making-up" to go out with Ste and Jamie at the end of the film.
Mama Cass Elliot did not die from choking on a ham sandwich. She had a heart attack. There was a partially eaten sandwich in the room when she died, but she didn't choke on it.