I knew nothing about Tesco Groceries Online! Thanks for providing that info. Re brown Chinese musheooms, my favorite ones are also sold by Tesco. See below:

"Tesco Finest Shiitake Mushrooms 125G
Tesco finest* - Find out more

Product properties
Suitable for vegetarians
£1.25(£10.00/kg)"

http://www.tesco.com/groceries/product/details/?id=273664769

Re Morrison's white potatoes for price comparison with reds, click the link below.

http://www.hotukdeals.com/deals/morrison-s-12-5kg-white-potatoes-2-instore-only-2471394