onion sets and seed potatoes

you will certainly get varied response from here on putting in supermarket stuffs. I would be very careful on them as they would carry disease (not fatal if eaten  but for growing). thats why we pay a premium on certified seeds from the producers.

If we buy small onions (sets) and small potatoes (Seeds) why cant we just buy new baby potatoes and a bag of Asda smart price onions (which are smaller than normal) plant these out and the potatoes grow more baby new potatoes and the onions just grow bigger?

the onions acts as reservoirs for sprouting and put whatever it has in new plant the final bulb will be a new one (you wont get a bigger bulb from the current one I think)
with onions they might carry allium virus which damages your plot to greater extent.

on potatoes different potatoes grows/produces different all over UK. because we have varied climate all over. It is better (if you want a good produce) to get a proper certified seed potato which grows well in your region.

A lot of supermarket veg is treated to stop (or slow) it sprouting. I think that if it worked well, we would all be doing it as a matter of course and seed suppliers would go out of business. My preference is to buy certified seed, then at least I know it will give me a return for my investment (assuming the weather and critters on the plot don't interfere  ).

I should also say that I'm always up for an experiment or two... 

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Planting an onion will not produce more onions....it will only produce a flower and then a seed head. As kleftiwallah says, you can save the seeds and grow onions from seed in future years if you wanted to do that.
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sorry to be a bit thick herre but if planting an onion does not make onions then how do everlasting onions work?

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Planting an onion will not produce more onions....it will only produce a flower and then a seed head. As kleftiwallah says, you can save the seeds and grow onions from seed in future years if you wanted to do that.

sorry to be a bit thick herre but if planting an onion does not make onions then how do everlasting onions work?
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It is an allium family which looks/feels/taste like onions. onions/shallots/welsh onions/garlic are from allium genus but different species 

Thanks all, yet again you are all stars.

with onion white rot becomimg more prevalent countrywide (and once you have it you cannot grow onions at all) - I really don't think it's worth taking the risk