As said, found the problem today! Went out and jumped it and it wouldn't have any of it....
Step Dad checked the cam belt and it's gone! It's sheared teeth off the belt (About 5 in one place missing) which explains the knocking noise, I suppose the belt slipped every time it got to that part? So - may well be looking at new valves again. The cam belt was supposed to have been changed when my brother owned the car, so we're going to rake out the receipt and find out when it was meant to have been done and who by and if there is damage hold them responsible!! My big brother said if they were meant to have done the belt, then there's no way they did do it because they don't just lose teeth like that.
Although I Don't much about it, the belt does look old! So that's another lesson, I'll always check the said work has been done in future!!!
In a way - and I know this'll sound odd - I'm so glad we've found out the problem and at worst it'll need the valves doing!!! Seems now like the oil being low was coincidence, and so it isn't the big ends so not so serious - AND I'm so made up that it wasn't my fault if you know what I mean? I was so gutted thinking I'd done damage, and now I know I haven't I'm really pleased.
I knew it didn't sound like big bearings - but I didn't know enough about it to think to check the belt! Quite nice to be right in a way and so glad it's not that!!
So now the car will have a cam belt and we'll see what damage has been done, then the oil change will have to be done, then after that I'll get the new clutch sorted and fitted! So some money to be spent, but worth every penny.
Thanks to everyone who posted on here trying to work out what it was with not much info, that's what I love about this forum, people always willing to help out.