I'm sure that in a world where we are competing with 27 other countries for haulage companies time and services that this will help hugely (along with the £300 KAP, lack of toilets etc etc):
In some ways I like this policy. Truck parks aren't free. Shouldn't the users pay for it? If you are exporting via rail and need to park your train for a while you will need to pay more directly for the siding use.
I think one thing you need to factor into your calculations is whether you are enthusiastic about fighting other UK Citizens over who gets the last turnip.
I'm sure that in a world where we are competing with 27 other countries for haulage companies time and services that this will help hugely (along with the £300 KAP, lack of toilets etc etc):