Seat Leon car not starting and then loss of power when driving

I recently bought a 1.6s Seat Leon privately. After a week of so i went to start it, turned the key and all of the electrics came on as usual but other than that complete silence. The starter motor made a clunk the first time i turned the key but then nothing after that. As i said the electrics were all fine and there was no fading or loss of power and the car will not jump start only bump.To begin with it would only happen around once a week but now its pretty much every time. At the same time ive started to lose power as i'm driving. The revs will just drop away. i change down gear and put my foot right down. sometimes it picks up sometimes it dies. if it dies then it never starts again, this is also the case if you stall.It happens whilst moving and also in idle at traffic lights, junctions etc. Basically the worst possible places :/ Ive also noticed what i think is a lack of power in the lower gears and that you cant go in to the red on the revs at all. it just bounces at 6 to 6500. The only other thing ive noticed is that the battery light flickers as im driving along and get worse as the power fades. At first i thought the non start and the power loss and dieing could be 2 separate problems but they both have gotten worse together to the point where its undrivable. Ive taken it to 2 garages now that have connected it up the the diaognostics and found nothing and had no real suggestions. Would greatly appreciate anyones ideas/thoughts. Thank you