When I open up Google I often see on the search history items that I would never search for, ie: this evening boxing match and football results where shown on the search of which I or my wife have got absolutely no interest in. Therefore, does this mean that someone is using my WiFi which is password protected and if so how?

more likely, your connection has dropped, and reconnected, using a new 'ip address' and you are seeing terms used by the previous people who had that address.

Have you left your Google account logged on a work PC etc somewhere?

This would explain it..,

[Edited on 1/5/16 by joneh]

I noticed that,on my mobile connection that i know is secure. I believe it's just Google suggesting popular current search terms.

Cheers guys, still a bit of a mystery though, I have only my personal devices at home as it is where I work from and it seems strange that Google make suggestions on so many subjects that I have shown no interest in. I can only think that it is what gremlin 1234 suggests. Thanks again all of you for your ideas.

[Edited on 2/5/16 by LBMEFM]

If Google is suggesting these as search terms, it's possible it's just doing projection base on your location etc. However, you can always go to https://history.google.com/history/ and look at your actual Google search history. If there's anything there that you don't recognise, then someone is logged in using your Google account and I'd suggest changing your password

D