I suspect you're going to (carefully) have to take the plastic trim off the hatch and inspected the doodah that operates the latch. Many call it a solenoid but it's really a motor that via a worm arrangement pushes out the white plastic plunger/push rod that operates the latch. My guess is that the white plastic bit has broken and jammed in the out position, or the return spring has failed. Either way, this would be a replacement 'solenoid', which is a common enough failure. (I did fix mine with a teeny threaded rod and epoxy).
Thanks for the reply Heaven - I've come to the same conclusion. Attached below is the reply I was going to post tonight before I saw your advice to me,
Also thanks to RGWM - think it is the solenoid I'm after
A late update since work got in the way last week. Reporting the cause in case others have the others end up reading this post.
After stripping the boot trim off I realigned the components several times, but no luck. Eventually identified the cause, more by luck that brain power.
On putting my fingers behind the latch I found that the release plunger isn't fully retracting to the closed position, so holding the latch mechanism unlocked. Pushing the plunger all the way home got one latch and one release. The plunger doesn't return to the fully retracted position. The attached photos show the extent of the problem.
I'm assuming that the fault lies in the plunger and not the spring in the mechanical latch not being strong enough. Working on this basis is there an easy fix or is a replacement required. . If a replacement is required any good web sites where I could get one (either new or 2nd hand) at a reasonable price?