Top fixing loo seat issue

Ganga

It sounds as if the fitting is sitting too low in the toilet pan ,when the seat comes down it is lifting the pivot to match the seat hight ,is there not any spacers supplied with the fittings to suit all seats.

nofoollikeold

1. That looks like the fixings for a top fix WC seat.
2. As you appear to have access to the underside of the pan, I suspect it is the wrong type.
3. Try using a a stainless steel nut (and washer(s)) and get rid of the plastic.  You'd have to check it, but those threaded bolts are usually M6.  If so Screwfix item 6386T would do (although rather too many), together with 235FT, again far more than you need.  I'd fit a nylon or rubber washer between the underside of the pan an the washer.  

NornIronRose

Thank you both. Turns out that sitting on it has helped somewhat. 
I've been in bed with covid so it hasn't been a priority. 

I do have access to the underside but it is really difficult on one side. Surely this should work for either.  

Will have another look at it tomorrow as I just need to adjust it slightly but it is sitting firmly for now.