Working for Warwick Manufacturing Group in the mid 90's I spent a bit of time in Rover and with some of the employees.
I had several as lease cars through the Rover leasing scheme and eventually owned a 25 for a few years too.
They (Rover/BL etc) had their good and bad times. I've read and heard many reasons why Rover eventually failed and struggle to completely understand why.
In the 70's BL became complacent. They believed the British public would buy a British car over any other. They IMHO produced some right old sheite, such as the LegOver and Maxi. Maxi was possibly ahead of it's time (hatchback with five gears) but still looked a pile of crap (to me anyway).
Unions and management fought like cat and dog right through the 70's and a good portion of the 80's.
Someone commented about government help. BL had it.
BAe were also a shareholder, in fact the insurance underwriter for the lease cars we had was indeed BAe.
I've even heard Jeremy Clarkson blamed for their demise :lol:
BMW gave us the rover 75 (well they played a part) and I never understood why. Maybe the design work had already started prior to BMW but the 75 competed with BMW models.
They wanted Mini of that I'm sure. That original New Mini was essentially a British car.
IMO Honda were always their best allies. They turned Rover around. There must have been some big bonus for someone when BMW bought them. Honda of course pulled out of Rover at that time.
In essence they built some **** cars and were managed badly by both owners and unions alike.
Some links to read. The ARonline ones being the best IMO
https://en.wikipedia.org/wiki/British_Leyland
History : British Leyland, the grand illusion - Part One - AROnline : AROnline
History : British Leyland, the grand illusion - Part Two - AROnline : AROnline
There are further parts on ARonline.