Brian Moris responded to my request on the last post, he has sent more information and images. One of which is the Marks & Spencer Blister pack containing 10 x second class stamps.
You will notice that the price for this pack was £2.00. Brian informed me that he thinks this was issued at about the same time as the 10 x 1st pack shown in the previous post.
Brian also attached a pair of the original 1st class retailer sample packs showing two different values. The £2.50 (1st class 25p) was issued from about late 1993 and the £2.60 (1st class 26p) was issued in 1996 the same time as the M&S packs.