Posted: 15/08/2013 at 11:24
The taste and smell tests suggested are absolutely not safe! Sorry for shouting but some of the deadliest mushrooms will easily pass these tests. There are lots of other "old housewives tale" tests which won't save you either such as if animals eat them they are OK for humans, if you can peel them then they are safe etc. Taste and smell can be used to help identify particular species but they are not safety tests.
The safest method is to use a genuine bona-fide expert if you can find one. (Living in France or Italy makes this easier, try the local pharmacist in these countries) Failing that you can try identifying them using several good books. I cross-reference using at least three books and will also check several sites on the web. I also limit my consumption to a few species which I can reliably identify. Any doubt and the're out!
One useful and easy test you can make is to take a spore print. Place the cap gills down on a piece of paper overnight. In the morning you should have a nice pattern of spores which you can inspect for colour to aid identification.
Your photos look like field mushrooms as others have said. However I don't have them in front of me to make further checks and more importantly you don't know me so how could you trust an internet stranger to identfiy something which might cause you serious harm?
The most likely source is that someone may have used spent mushroom compost in the garden and this will often still have viable spores in it giving you an unexpected but welcome crop. If you have pastures near by then this may be the source of the spores. Exactly where mushrooms grow can help with identification too.