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They might well be, here is the guidance from Hargreaves Lansdown:
'In 1978, British Leyland became BL and in 1986 was renamed Rover Group. It was then acquired by British Aerospace in 1988 for £1 a share or you could have one British Aerospace share for every 4.93 Rover shares held.
British Aerospace, now known as BAE Systems, split one into four shares in 1998. These shares are still valid today, trading at around 449p.
Assuming you have not sold your shares or acquired additional ones through scrip dividends - where you take new shares rather than cash dividends - you should have 812 BAE shares worth about £3,645.
To confirm your holding, contact Lloyds TSB Registrars at The Causeway, Worthing, West Sussex. BN99 6DA or call 0870 600 3989.