Service providers like retail outlets arrange to have wild mushrooms picked so that they can be sold off. Those who are familiar with this type of fungus however will know that not all of them are fit for eating. There's no need to worry though, as companies are well informed on which kinds are safe and those that are off limits.
Within the UK, the safest wild mushroom is without a doubt the giant puffball. It's possible to confuse them with other breeds when they're smaller, so you should always wait until they fully mature before harvesting them. Strong in flavour, this mushroom is an excellent addition to a meal when cooked correctly.
The hedgehog fungus is named that because of the spikes that grow underneath it. Another completely safe species, you can tell a hedgehog fungus apart from other mushrooms with spikes since theirs are white, a colour not found with different classes. The spikes supply a minute level of culinary worth, so you should scrape them off before taking the mushroom back.
There are more mushroom groups out there aside from the ones mentioned here. Each is unique in their own way, so be sure to discuss your requirements with a professional if necessary.