I have taken boat parts to an from mallorca many times.

Radios, auto helms, oil filters as well as thumping great zinc anodes which could do all sort of damage if you threw them - far more than a pen knife - but Anodes and marine radios are not on their list so they just let it through.

I did once take a tube of areldite through and they confiscated it so maybe they thought I was going to glue someone to the seat. Any tool of any kind will get taken off you. Screwdriver, spanner etc - but at Stansted they let you goto the post office at WH smith, buy and envelope and give them to the customs guys with a stamp and they post it home! You know how I know!

The rules dont really have much to do with risk, they have a lot to do with what is, or is not, on a specific list.