It's true but if you sign up for an account it's only £1.67 per crossing.
The disadvantage with opening up an account is that you're meant to top up by £10 to open the account. I somehow avoided it though

I'm not sure what happened but I cancelled out at the payment stage and it ended up creating an account for me with 0 balance. I then went to top up manually and it allowed me to put any amount I wanted on - so I tried adding £1.67 on for one crossing and it added it to my account. The crossing shows up in the history on the account so it's all good.
I'll probably just keep a fiver or so on my account just in case I ever forget.