[JayG]

I gave away two spare pepper plants sown from the same Wilco's packet to my neighbour; one of them is producing fruits just like mine, the other one is producing peppers much more like those on the packet picture; currently green but will no doubt go through some sort of traffic-light sequence as they ripen.

Despite losing one or two stems which snapped clean off taking their immature fruits with them (  ) mine still seem to be doing OK, and they are now not all yellow:

[Nobbie]

I used the same seed from Wilkos and most of the plants are like yours, but I do have one which is the more regular box shape and green colour. The seed is mixed peppers, but they don't show the long yellow ones on the front of the packet. It will be interesting to see how they taste!