Thanks for your question, I would caution this will not be easy reading you I regret to say.
The difficulty in terms of her naturalisation is that the requirements are residence for 3 years for spouses of UK nationals and 5 years for anybody else. Obviously, she qualifies under both of these criteria so even if she were not married she would still be entitled to be naturalised. We don't know how she applied for naturalisation (ie. As spouse or other). Even if she applied citing herself as being married the criteria is that she is married to a UK citizen, which she technically was.
The UKBA only take enforcement action in respect of revoking a person's citizenship in most serious circumstances where it has been obtained fraudulently. In my view I cannot say that it has. You can attempt contacting them to see what there view is but I should think they will take a pragmatic view because they are so over-stretched in other areas of immigration enforcement:-
It would also have the disadvantage of inflaming her approach to your divorce.
A marriage of your length is considered a "long" marriage for the purpose of matrimonial settlement. This means that all assets of each party including those ac quired before marriage form the matrimonial assets pool over which a financial settlement must be agreed (either privately or via the courts in ancillary relief proceedings during the divorce process.
There is a presumption in long marriages that each party shall receive 50% of those assets. This presumption can be rebutted largely if there are minor children that shall reside with one party or, to a much lesser extent, if one party requires more income/assets because they have a health condition that requires this but in any event it is difficult to see that a Court would depart very far from a 50% split I'm afraid.
I would take specific advice from a local divorce lawyer on this after confirming all your assets and hearing what the UKBA have to say. It may be that you accept that she is entitled to a portion of the matrimonial assets pool but choose to negotiate informally with her by appeasing her with less than 50% for the sake of being amicable and thus obtaining a better settlement than you could reasonably expect at Court during the anciallry relief divorce process.
I am very sorry it could not be better news and you have my sympathies.
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