That will be down to the UK government not NATO.
It is certainly possible. But our current military leaders have made it clear in the past,
1 career milatary volunteer is worth 100s of untrained forced fighters.
The cost of training huge numbers of conscripted fighters. When fighting a modern battle. Is not going to be the first choice of our military by any means. Moving from a total voluntary army to conscription would take a huge change in our forces. More so then the US that at least still keeps records suitable for drafting young fighters.