Yes, all these ABers are right, the price of them is now 42p, and I think they were 30p when they went off the market. I can remember in 1988 they were about 17 or 18p. Those were the days.
The process of reducing a product's size is called "downsizing" ,and unfortunately for us poor old consumers completely legal. They have gotten round this rather medieaval practise by putting the product weight on the packet and it is up to you to look at it, and compare it mentally to the former weight. The price of this product usually remains the same, and presumably it is done to avoid a price rise, although not in this case. Full size Mars bars are now blatantly advertised as this, as for quite a while they went down to the low weight of 54grams. What a rip off!