If your circumstances have changed then you are well within your rights to request a change of circumstances review.
CM is for all day-to-day living costs of the children - this includes: school uniforms, school lunches etc etc. Other expenses such as trips etc should be split equally between both parents.
Of course you are free to add anything else - if you can afford it. There is no point in bankrupting yourself!
My first port of call for advice would be NACSA (national association for child support action). They are a non-profit organisation who provide the most up-to-date advice and support on all CSA matters. They know the most up to date legislation and all the tricky lies the CSA will also try to tell you. They will also do a full assessment for you. Membership is about £45 a year, well worth it IMHO.
From what I can garner;
- If you have a court order directing payment of child maintenance (which are usually set at higher rates) then there is nothing to stop you from writing to the Court to seek an opinion about a variation in maintenance due to a change in circumstances. Such a letter would be written to the Court where the order was made, addressed to the judge (phone up to make sure the judge still works there!), with your case number in the top right.
- If the order is over 12 months then as I understand it (bearing in mind I have no formal legal qualifications) then the Court would normally suggest the CSA is used. Again the procedure would be to write to the Court, seeking an opinion, stating that there have been a change in circumstances since the order was made (i.e. change of salary, more children, number of overnight stays etc) and you respectfully request an opinion from the Court on how to progress. You suggest that either the CSA/C-MEC is used for child maintenance matters or you and ex-partner come to a private arrangement, using the CSA/C-MEC guidelines for figures.
I understand your feelings about the ex's lifestyle etc and the children asking for pocket money. Kids will play one parent off against the other and try to maximise what they can wangle.
IMHO I would suggest writing a letter to the ex stating the current situation regarding CM, that you feel it is time for a review especially due to the change of circumstances.
You would then suggest a figure that is in line with the CSA/C-MEC guidelines.
Stress that you feel it would be beneficial for everyone to have a private arrangement.
Request a reply by 2-3 weeks ... and see what happens!
In the meantime write to the Court seeking an opinion.
If you want to discuss off-forum feel free to PM me or email.