I have, however, recently resolved the problem - and the solution is a little embarrassing - but I'll share it here for the benefit of anyone else with the same issue.
Quite simply, one of the function keys on the laptop has a 'switch the mouse pointer on or off' feature. This is something I have never seen before, despite having used laptops since they were practically first available.
On my particular laptop (Toshiba Satellite L855) the F5 key does this. It has a picture which is hardly identifiable as a mouse with a line through it.
Press this (or press FN+F5 depending on you configuration), and hey presto... the cursor returns.
Thanks again - and hope this helps someone else.
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