Serco is well aware of the GCAA salary increases and there is a meeting this week to discuss their reply.
Since Serco stands to lose either way with their reaction: a) Don't give any salary increases and have controllers cross over to the dark side thus losing those controller positions (and $$ as result.) b) Increase the Serco package and take that money off the bottom line; I would anticipate Serco to delay their official response by at least a month (disguised as "high level meetings") to put off the inevitable.
"IF" Serco wanted to claim any sort of respectability in this situation, they should realize that they cannot find a winning edge in this predicament and make their decision promptly. This would show me, for one, that Serco had already anticipated the GCAA pay raise, (which they should have) and had already prepared a response plan ready to be actionned.