Hi bubber - I don't normally post much but in the case of this abysmal puzzle I think full disclosure, not just hints, is called for. So, for 1a you have either CONSTRUCTER or CURRENT-COST. Previous posters have said only that it begins with a C, as though that will be helpful.
The trouble with Poat is always that he thinks he's so clever. If you're a Listener devotee you'll remember him for the 'hare' puzzle in which the endgame took place within the preamble, outside the grid. See what I mean? There's just too much work involved in this one to make it worth continuing. You'll apparently end up with a completely different grid apart from the unches in down clues, which even at first solving are often impossible to fill.
Add to that the fact that 6dn is pointless as you get all the letters without having to dig around for an obscure anagram, and the unfair over-unching of 6dn and 17dn. Over-unching of downs crossing 1a is at its most absurd in 7dn, effectively a 3-letter word with two unches!
Dr Who fans seem to like it though. Some of them have solved it.