Not as far as I've seen, standard UK contract is typically has something along the lines of IP created "in the course of your employment" (i.e excluding unrelated work).
Although if you're working on particular open-source or startup projects on the side you should just get a specific clause inserted into your contract which excludes those projects.
That's what I recalled from when I read through it before signing (evidently not in close enough detail...)
However, the phrasing is: "any invention wholly or partially made by the Employee at any time during the course of his employment with the Company (whether or not during working hours or using Company premises or resources, and whether or not recorded in material form)."
"during the course of his employment" restricts it to works made as part of your work duties. Obviously this can fall into vague territories though if your day job is in anyway related to your side projects, so I'd still recommend you get a specific exclusion for any side projects.
Although if you're working on particular open-source or startup projects on the side you should just get a specific clause inserted into your contract which excludes those projects.