Thanks for all suggestions so far. Point I should have made about
the placement of the two large caps is that the motor just needs a
flick to turn a cam every 15 seconds, and there's just enough juice
in the 3300u to do that. It's a tiny motor that takes 50mA.The 470u
is the PSU reservoir. The 3300u is isolated from the PIC supply by
the 2k2 so that when the motor drains the 3300u it doesn't take the
PIC supply down as well. So far I haven't had any problems with
resets but the addition of other cheap components to preclude this
and others to protect the PIC from spikes or over-voltage is good
practise and means hopefully I'll never see it again as well as having
a happy customer.

Jinx