Not sure how this has happened but when I open up Google search on my laptop, it is coming up in my partners name i.e her Google account and hence I can see her search history etc!! No secrets hey!!
This was only noticed when I clicked on a link a company I'd recently used sent me an email with a link to leave a review for them. When I clicked the link it brought up a page to leave the review via Google, and it was my partner's name that appeared at the top eg it had opened it up via her account.
Like I say no idea how the switch from my account to hers has happened, but clearly I need to switch it back. We don't have any secrets - well not now, but joking aside, this aint right!!
Thanks for your answers, which have helped me solve this. I've done as suggested, signed her out and myself back in. Yes she did recently use my laptop and it must have "remembered" her.