It is dog lichen and growing prolifically due to the poor drainage and over compaction of your garden. The compaction is made worse by the fact you cut it with a roller although this is not responsible merely a factor.
You need to consider either a proper drainage system which will be very expensive or as a first step try hollow core aeration. Then brush grit sand into the cores and top dress with it too.
There is no point killing the lichen which any moss killer will do unless you sort out the drainage.
Fungus' lichens and algaes have been extra ferocious this year as its been so wet and warm.
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local