Plastering and insulating wall with boiler

[Hl.house]

We need to insulate and plasterboard an external wall. This wall is approx 4m long and the boiler sits on this wall approx 50cm away from the corner. Any ideas what I can do to plaster/insulate/box the boiler space?
Picture below:

 

[cjard]

Either take the boiler off the wall and insulate behind it (better), or build a doored box round it and insulate that? It looks modern enough to have an anti-freezing capability. Moving it would be a good opportunity to sort out that rats nest of ad hoc piping too