Why am I being charged £1 for occasional transactions?

[Darkskynet1]

I sometimes get charged £1 for transactions. 

Recently I was charged twice for 2 x Uber transactions (£1 each) on top of the price of the ride, these appear as separate transactions on my statement. Does PayPal charge you for paying using its service?

[sharpiemarker]

@Darkskynet1 

They are temporary pre-authorizations by your card company giving the merchant the okay to charge your card for whole amount. Its like validating the card you might say. Authorizations can be with £1 or the whole amount. They chose the £1 option. They’ll expire and drop off eventually.

The dark side to this is fraudsters may do these validations to test a card so if you randomly see these authorizations out from nowhere nor from any actions you took related to them (ie. making a purchase, updating an expired card), that can be a sign of a compromised card.

[Darkskynet1]

Thanks for your reply, so by "drop off/expire" does that mean I won't get charged the £1 for these transactions?