Hi, I have just been through this process. The formal way for them to look at other income is to request a variation. Do a detailed letter of your reasons why you think he is earning more money than declaring with as much evidence as you can. Screen shots of Facebook holiday pics showing date and location etc. If you have already done the official variation request I would sent it to your local MP to act on your behalf. I just did this and after getting nowhere myself for over a year this was sorted after just a month. Once the variation is complete and if you are still not happy with finding amount you can then request the case gets put forward to the Financial Investigation Unit. It can take around 6 months but they will look at bank accounts, diversion of income etc. Hope this helps.
