The following blurb I've seen in Go Outdoors shop as part of a promo board but is also on the website:
Nothing new in that you might say- but what drew my attention was this bit of text
The extra security also gives you the peace of mind to go that little bit faster and have even more fun!
So it would appear, you can go faster if you wear a helnet- allegedly. Given what we know about the limitations of cycle helmet design, this is not a claim I'd be tempted to put to the test- lol.