Um why is this only rated 15 in the UK?

There's another thread that probably covers this better, but in fact the film was originally intended to be much stronger. The distrbuters however wanted a "15" certificate so they sought advice from the BBFC during post-production on what edits would be needed:

During post-production, the distributor sought and was given advice on how to secure the desired classification. Following this advice, certain changes were made prior to submission

This film was originally shown to the BBFC, for advice, in an incomplete form. The BBFC advised the company it was likely to be classified 18 but that their preferred 15 could be achieved by making reductions to a couple of scenes of crude humour. When the film was submitted for formal classification, these sequences had been acceptably reduced.
http://www.bbfc.co.uk/releases/grimsby-film
(Click on the down-arrow for "Precuts information".)

The US release is actually an "R", not an "NC-17", and that's quite common for UK "15"s (although there can be some variation "around the edges" of those categories. Having said that, I've seen suggestions (but can't confirm) that the US release was toned down slightly...

--
"So I've got bullets, but no gun. That's quite Zen."

Here is the BBFC Insight on Grimsby from their website:


GRIMSBY is a comedy about a pair of estranged brothers, one of whom is a secret agent.

Sex

* There are strong verbal and visual sex references, including to oral sex, masturbation and ejaculation. Some of the references are crude in nature, although they occur within comic contexts.

* There are a couple of sex scenes, both of which are comic in nature and lacking in strong detail, although there is sight of pubic hair.
Violence

* There are several scenes of moderate action violence, with occasional stronger moments including some focus on blood spurting as people are shot.

Drugs

* A character accidentally injects himself with heroin and later expresses the view that the experience was better than expected. However, the comment is comic and the film as a whole does not promote illegal drug use.
Language

* Strong language *beep* as well as milder terms including 'twat', 'bitch', 'bastard' and 'bollocks'.

There are also scenes in which lit fireworks are placed between buttocks.

There is some strong comic nudity.


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UK and USA tend to have different about what is appropriate for different age levels. UK tend to go much easier on nudity and sex and are much tougher on violence (especially violence that is considered imitable, or violence that is glorified or dwelled on in detail). The R-rating as a whole is also not as lenient as a British 18 certificate (as 18 ratings also cover the US NC-17 category).

The BBFC have a page talking about the difference between the classifications:
http://www.bbfc.co.uk/education-resources/education-news/same-difference

Funny thing: Here, in Germany, it has a 12 Rating. Which also means, that 6 year old kids could see it, if they go together with an adult friend or family member. The owner of my local cinema gave the advise not to listen to the official rating and recommended that you should be at least 16.

MUSLIMS

They went all the way in this movie, so i can't understand that something could have been cut at all.

There will probably be a extended version with deleted scenes, so i need to see it again.

lol so you think someone who's 17 and can legally have sex and join the army to kill someone shouldn't be allowed to see graphic violence or nudity ?