That's because you've 'carted' it with only 1 item! ..... If you order more items from Restormate it's still the same delivery charge. Their a B2B supplier so like most others, they're not really intending single items, couple o'quid purchases I guess.
What I would say is that they are lightening fast - noone is quicker in my experience. They use Fastway. I am about 25 miles from Restormate's premises and I placed an order for some Catalyst at 8.30pm on Tuesday night; it arrived at 2pm the next day!