You'll find the London end of security a lot more of a pain in the neck than the TSA... But if they're checked it should be a non-issue. Since tools aren't a danger to the Aircraft and aren't illegal to bring into the country.
My largest concern would be customs... If you're coming in on a tourist visa but bring work tools with you they might suspect you are attempting to enter to work or to stay.
Make sure you have a local contact number for your "friend" and that they can backup everything that you will say. If you work in an industry associated with the tools then it might be even more of a hassle.