An ultraframe roof by looks of it. Lost count of how many of these I've fixed but most roofs are the same but unfortunately it means everything needing to be sealed is on the outside. Ronnie is right that there's a foam bung above the ali plate where all the rafters push into and seal, 9/10 the leak is down the centre of the bung, easiest things to check first is make sure all the sheets that meet around that junction are pushed up and not slipped down, hard to tell at the top because they go under the semi circular crown so check along the bottom, are they all in line, is one a couple of inches lower?
My procedure would be...
- Remove the spike from the outer crown, should unscrew
- pop out the 4 plastic clips holding the crown onto the main ridge capping, this should have been siliconed on so will be tight to slide off
- now you should see the foam insert/bung and in the centre you could possibly even see down into the conservatory
- belt and braces this part, slide the first section of finials out of the ridge cap, clean and dry the channel
- apply silicone in channel and slide finial back in
- with expanding foam fill the centre of the foam bung and anywhere around the rafters you see that looks suspect
- from here slide the crown back on making sure to applying silicone to the ridge cap before sliding crown back on, then screw together and use white screw caps because you probably snapped the 4 plastic clips
- before screwing the spike on seal the end of the finial where it meets the spike, put a big thick ring of silicone around the brass threaded insert and screw the spike on
In some extreme cases I've had to slide the complete ridge off to seal it against the house wall, means internal crown off, which you already have, internal ridge off, ceiling fan off if you have one, down lighters too, vertical tie bar if you have it, remove plastic wedges by pulling down on threaded plastic rods, this releases the ridge which then needs to be slid off the front of the roof, it doesn't lift off, now you can do your investigation
You can see why a lot of companies won't touch conservatory roofs especially ones they didn't fit because it can be very difficult to trace leaks and they don't want to buy someone else's problems