The ECB advice is very grey, and not clear at all. This is not classed as work or an essential journey if you are a volunteer.
The Institue of Groundsmen offered more advice on the 1st April
"Volunteers should follow latest Government guidelines and not put themselves or others at risk. We advise that the volunteer network monitors the timings of any announcements of the various sports re opening for play, however realistically this will be dependent on how we are able to slow the virus down and return to normality."