ok...can confirm that the car is now driving once again
i did find this quite hard to do,,but it is done, and now that it is, i can tell you all something funny, which shows just how much of a novice i am: when i was first trying to remove the first downpipe to manifold bolt, i was under the car, trying and trying so hard to turn it, soaked it with plusgas few times tried and tried, whilst holding the other side of the bolt with another spanner, then after probably about an hour of trying over and over, i was laying under the car, and i thought,, wait a minute, am i turning clockwise or anti-clockwise?? it took me a few moments to figure out which was which because of my position, then i realised, i had been turning it the wrong way all this time!!! i was turning in the tightening direction!
anyhow, that all out the way, have put it all back together securely, driven for about 300miles since. it seems to be working okay thankfully
thank you all for your help!