I had a bump whilst insured on my partners insurance, do I have to declare it when looking for my own policy?

Did you make a claim when you got that bump? If yes, then you would need to declare it.

Even if you have reported it to your previous insurer, it goes on file. So the moment you make that call to inform them, this information is recorded on your policy and whether you decided to make a claim or not does not really matter. That's why many people choose not to inform their insurers when they can afford to make the repairs themselves, otherwise they are faced with higher renewals.