Dick, I disagree with your assessment.

It is very rare for a governing party to take votes from opposition parties at by elections.

Labour previously had a large majority in both seats.
We saw a large swing away from Labour, a small swing to Ukip and a large swing to the governing party which is an extraordinarily rare occurrence.

Hence my assessment in the OP,
"It looks like a disappointment for UKIP, a catastrophe for Labour and a triumph for the Tories. "