Re: Indeed...
"My default view then is that I'll leave early April"
Be careful
The draft legislation says that any *payments* made after the rules come in are subject to the new rules. So, even if you terminate the contract at the end of March, if the invoice isn't paid before 5th(?) April the new rules apply and (if they have determined you inside) will be paid net of taxes.
Also, although HMRC say they won't use status under the new rules to open investigations into previous years.... Does anyone believe that? IMHO if you were operating outside and then accept an inside determination with the same client, HMRC are likely to say that meant you were inside in the first place. Hell, I wouldn't even move from outside to umbrella for a current client, or accept an umbrella gig with a recent client I've worked outside for. I don't trust HMRC as far as I can spit!
Most contractors I know are saying they will terminate their current contracts by the end of Feb to ensure invoices are paid before the new rules come in unless they receive an outside determination.