Poppers don't last very long. The most common types here in the US are Isobutyl Nitrite and Alkyl Nitrite. There are many different brand names but almost, if not all, all poppers are one or the other of these two compounds. originally poppers were amyl nitrate, but while that compound is still used for medical purposes, it is not easily available for recreational use.
Isobutyl Nitrite tears the skin around my nose to pieces so I don't use those. I have less adverse reaction to the alkyl nitrite.
I like using poppers and use them in JO sessions and while playing with dildos for fucking myself in the ass. I also like using pot while using the poppers for a very fun and exciting time.
Too much poppers can affect your ability to maintain an erection. And using poppers while take drugs for erectile disfunction can be very dangerous, even deadly due to causing a significant drop in blood pressure.
There are lots of online sources for poppers. I don't know if they ship to the UK but I've found
Anon URLto be a good source for reasonably priced (compared to sex shops anyway) poppers.