30% off at Marks & Spencer tomorrow?

Sarah Coles
Marks and Spencer stock
Marks and Spencer stock

Rumours are spreading that Marks and Spencer is set to stage a one-day sale tomorrow, offering 30% off a huge range of goods. It won't be the only chain to launch a pre-Christmas sale this week, but it will be the first time since 2008 that M&S has joined the fray.

So why is it doing it, and where else can you catch the sales?