I went through here yesterday and both platforms are reduced to about half width by plywood shuttering. Anyone know what they're doing behind there?

Possibly something to do with this . . . . .

Taken from Wikipedia

In early June 2014 it was announced that this station would be among a small number of stations on the Merseyrail network that will be spruced up as part of a £3.7m programme of improvements. In May 2015, the ticket office closed for refurbishment works to take place, which reopened in June 2015. On 15 June, work started on the platform areas. 6 Car trains did not stop at the station between 15 June and 20 July whilst some of these works took place.[1] Work is still ongoing with the platforms being extended to allow passengers to have more platform area. New Waiting shelters are also being built, replacing the existing ones, as well as new lighting and information boards.

Thanks, Habdab.