We flew with flyglobespan in the October half term just gone. We selected seats/meals as soon as the booking reference came through (though we only booked about 10 weeks before our holiday). I would give them a ring to check.
We were in premier economy on the outbound, and economy on the return. By the time you add the seat selection, meals, and drinks to the economy fare, premier is very good value, but the seats in that cabin seem to sell fast. Service was good, landed early on both journeys, the only negative is the lack of seat back tv system, but we would definately fly with them again - though I note their prices are significantly higher next year (we paid about £280 return inc tax, but it's a lot more now).