I got bell peppers of various colours that were bought in Tesco I believe and had a go at growing pepper plants from the seeds after I used the peppers. I watched them from seed in a small pot, transplanted them to big flower bed and they eventually flowered (yellow). The fruit however is tomatoes. I have 6 or 7 plants which all produced tomatoes. How? The plants were grown near actual tomato plants but this hardly is the cause? Any experts know any possible reasons? Thanks
Assuming you really are sure these plants came from the seeds from your supermarket peppers, what you have are tomato-shaped peppers. The only way to find out what they will taste like is to eat them!
Pepper plants grown for fruit will most likely be naturally cross-pollinated from different varieties growing nearby, and plants grown from the seeds will not be identical to the parent plant.
If you buy named varieties of pepper seeds from a seed merchant, the parent plants will have been protected from cross pollination to ensure that you get "what it says on the seed packet."