I've just recently signed my contract for my new position. The new position is with a government agency (UK) and works on a specified salary banding system.
My current pay is higher than the lowest pay point on the band for the new position, so I asked for the new employer to match my salary (moving me slightly up the pay band). They agreed to this - as per their policy - and I sent them my pay slip, then signed the contract stating that figure.
A couple of weeks later, and my current company had given all employees a not insignificant (~5%) pay increase, which would have matched me at least one pay point higher with the new employer.
While I understand that I've signed the contract, so the new employer has no obligation to match the new salary, I'm wondering whether to bring it up anyway. I don't want to be seen as a money grabber, but at the same time a 5% increase is a significant sum for me (6 years off my mortgage, for example, if I used it to over pay). Obviously I wouldn't mention the personal reasons, but I'm wondering about how reasonable it is to inquire about matching against the new salary.
What are some potential implications of asking for an increase at this time? Am I likely to find any success, or am I simply running the risk of upsetting my new manager? I made it clear to my new manager when initially asking for the salary match that I was willing to accept the position without it, and there's no threat of me turning down the new role if they do not agree: even if I hadn't signed a new contract. My only concern is souring the relationship or giving my manager worries that I'll be willing to jump ship for more money in the near future (I very emphatically am not)
As a final point, when I gave my salary originally on the application, the amount stated was for the current higher salary, not the one they originally matched.
Or in short: would it be considered reasonable or unprofessional to return to the subject of salary due to a raise at my current position?
Note: this is very specifically different to a typical salary negotiation during recruitment. The company does NOT negotiate on salary in the traditional sense. A position has a set pay band and a new hire starts at the bottom of the band. However there is a specific stated policy to match a recruit's salary. This is why I ask the question, as it is very different from the typical interview-offer-negotiate-contract cycle I'm used to, where previous salary is not relevant. The question is perhaps really better described as: Does the usual 'don't return to the negotiating table' form still apply to these circumstances?