It’s common. I’ve always asked employers to amend this and they happily oblige.
* "It's boilerplate; we can't change it!"
* "We never enforce it, do what you want."
* "Do what you want, who's gonna know?!"
* or some blanket legal statement: "Either your projects fall outside the scope of the clause, in which case you don't need to worry about said clauses, or they fall within the scope of the clause, in which case we are not wavering anything. And finally, its up to you, not us, to judge whether the project falls inside or out of said clause."
I've yet to come across a UK tech company (or R&D company) that has ever taken my concerns seriously. It's starting to bum me out. I don't want to work on releasable products knowing deep down that I might not actually own them.