I took a collapsable pole (fitness device) in my hand luggage out of LHR, with BA, no issues at all. Wasn't even flagged up as an issue through security.

When going through LIS on the flight back and got to security and it was flagged for secondary check. They were looking at it, called over more security agents and, at one stage, even a police man was looking at it. I was informed that this couldn't go through in my hand luggage, as it could be used as a 'weapon' and I had to go back out, to check-in and separately push it through. To be fair, although it was a very strange experience seeing three members of security and a police guy examining it, they were fairly nice about it and apologetic.

So, yes, even if you get out of the UK with it, you might find, like I did, you can't the other way around.