Been looking for a new cycle helmet and came across this on amazon last week on the daily deals. It is now back down to the same price as the daily deal and I thought I should post it in case anyone needs a new helmet. The helmet is the cheapest adult size helmet I can find anywhere, not to mention it is from a good helmet manufacturer. It is fully adjustable, with a dial adjuster at the back (just turn to loosen or tighten) and the chin strap comes with a sort of zip tie clip-in which means it to is adjustable.
There are two sizes (M = 52-57 and L= 56-59 cm) and three helmet colours to choose from (black/silver, white/magenta and white/blue/green).
The prices range from £13.22 to £13.76 for the three helmets (free delivery if you spend over £20 on amazon).
There is also the Alpina Panoma City Helmet (only difference I can see is the city helmet comes with a red light at the back) which is a bit more expensive (~£17-18) but comes in different colours which may suit you better.https://www.amazon.co.uk/Alpina-Panoma-Helmet-visible-reflective/dp/B015KOL39M/ref=sr_1_3?ie=UTF8&qid=1473411134&sr=8-3&keywords=alpina+panoma
*Also the price seems to change from day to day, so I guess this price will only be for today.