I have now been back to Morrisons in Winsford, and the price is indeed £2.49 ('While stocks last').
I don't know why I thought it was more expensive.
Meanwhile I have now bought some Birds Eye frozen soya beans. The TV ads for these have me most intrigued. They look like elongated garden peas or, alternatively, like bright green baked beans. I can't wait to find out what they taste like.