Safari crashes on first use.

I am having a problem with Safari. It crashes on the first use every time it loads.

If you don't do anything in the search bar when it loads you can do things like go to Preferences, Clear History, etc. But as soon as you go to a bookmarked website or click on the search bar and search for something Safari disappears and several moments later I get the "Safari quit unexpectedly message". Once this happens my iMac will then run really, really slowly and I'll get loads of beach-balling so the only solution is to restart. If I don't use Safari everything is fine.

I am using a late 2013 iMac with High Sierra 10.13.4 - when this started happening I downloaded the latest system update and security update but this made no difference. As far as I can see I have no plugins installed, I've tried Clear History, deleting Safari preferences file all to no avail.

Running Safari on another user on the same machine works fine.

Currently resorting to using Chrome but it is annoying that Safari won't work on this user. Any other suggestions?

Thanks in advance.