Because she's Swiss and has presumably registered herself back in Switzerland, she has the right to file for divorce here. The divorce would then be initiated here with the OP invited to participate here in Switzerland here.

I'm going to assume that in terms of agreeing an adequate sum for child maintenance, it would be more realistic to use the Swiss courts as they will have a much better and realistic idea of how much will be required to maintain a similar lifestyle post divorce

The UK it is then...

If the children are living in Switzerland then the Swiss courts have jurisdiction over the amount of child maintenance to be paid, regardless of where the divorce takes place. Child maintenance is based on the cost of raising a child in the country they are living in. This is fair (although if the non resident parent is living in another country this may seem tough, given the high cost of living in CH).

I got married in the UK, divorced in Germany (where I was resident whilst I was married) and child maintenance was decided on in Switzerland, where I now live.

Everyone talks about maintenance being a fixed percentage of income, but that was not my experience. During the hearing, the judge gave a verbal guidance of a fair maintenance payment of being between 800 - 1000 CHF (for one child). We were then encouraged to come to an amicable solution within this bracket. I suppose if we had not he would have fixed the amount.

All the best in sorting this out. It really is no fun.

as always the answer is .. 'ask a swiss lawyer'...

but 30% seems a bit high.... from similar experience, there are 'guidelines' but nothing hard and fast.. the (swiss) court will decide how much you should hand over based on the petitions you and your ex. make.... they'll take into consideration what % of time the kids spend with each of you.. and both of your incomes.. and the costs associated with the kids (but not any costs you have yourselves...)

but remember, in principal, after the divorce you're only paying child support, not maintenance for your ex....

.... and that's were the system falls down.. it's quite arbitrary... and seems to depend a lot on the judge and what he or she had for breakfast...

No. It is decided by the Courts that oversaw the divorce.
Swiss courts have no maintenance jurisdiction over a UK national, if the UK courts made the initial order. The best a Swiss court can do is enforce a UK order.
If there is no order in place then the Swiss national/resident has to apply to the court that has jurisdiction over the non resident parent. If that person is in the UK, then the petitioner must apply to a UK court. I have been in both positions and had this explained to me by the courts.

Child maintenance is not decided by how much it costs to raise a child, it is based on what the non resident can afford and how best he can provide for the child/ren. You cannot get blood out of a stone. Making an order to provide is pointless if the respondant does not have the means.

Well I speak from personal experience. My divorce was in Germany, but did not cover child maintenance (unusual, but it did not).

My divorce was in Germany because my husband filed first .... He won the classic race. However I could also have filed in switzerland where I moved too ... But he got there first (I didn't realize the importance of this at the time).

I had to go to court in switzerland (3 months ago, so all very clear in my mind) to get child maintenance sorted. The jurisdiction was related to where my duaughter lives and her needs. Fact.

There were 2 elements in deciding how much was paid. The needs of my daughter and the ability of her father to pay. But the judge told my ex husband that less than 800 would only be possible if he was able to prove he had very little income (which was not the case).

I am sharing this because I do think that personal experience is more relevant than opinion.

I will also point out that my ex husband is a non Swiss resident, ie, he still lives in Germany. There was never any question of whether a Swiss court could make a maintenance order for him. I assume this is covered by some cross-border convention protecting the interests of the child, which is what child maintenance is about.

In the absence of an order made in Germany, the Swiss courts could make an order if they could prove domicile. There is the REMO agreement to cover cross border enforcement.

thank you all so much for the responses, and apologise for the very late reply, our internet has been down and then I buried my head in the sand hoping it would all sort itself, I am currently looking at getting legal representitive in Zurich now to get it sorted as its not going to go away on its own, thanks again for all your inputs