I've been happily paying child support to my ex-wife for several years now, but we still have our ups and downs and she still occasionally shuts me out of her (and my son's) life if I piss her off.

My son has a major life event coming up later this year and I've been asked to contribute a four-figure sum (on top of the child support payments) to help pay for the weekend's celebrations. In theory I have no problem paying this, but in the light of her giving me the cold shoulder again last week I'm wondering if I can retaliate by withdrawing the extra payment and telling her to pay for the party out of the child support payments.

Can I do this? Will she be able to take me to court for the extra money? I don't really want to resort to this but I want to make it clear to her that I'm not just going to lie down and take it when she screws me around like this.

So, given that I'm happily paying child support, does she have a leg to stand on legally when it comes to asking for extra payments on top of this? I'm in the UK, as that will probably affect the answers I get.