Adding wife as an employee

[northernladuk]

a) my company's payment pattern to me has been very consistent for the last few years: the amount is mostly below the higher tax rate ceiling. If I add my wife as an additional shareholder, that pattern will change significantly as a much larger dividend will go out of the company. Will this pattern change attract the taxman's attention?

More than the original situation but probably not unduly. The change in shareholding is more likely to particularly if you have to change it again sometime in the future. You need to stay away from dividend waivers as well.

b) There is a lot of cash in the company which itself may cause their attention.

Why on gods earth do you think a company with a healthy bank balance cause attention? You are a tiny company and the money you are talking is peanuts compared to proper businesses.

c) My company has been trading for nearly 10 years, which may have a higher probability to be IR35 investigated. Won't start a new company be safer in IR35 land as it will only have a short trading history. Hopefully, they won't pay much attention to my dormant company which I can close in future.

Again I don't think this is true. IR35 investigations come off the back of other ones such as a tax one. Opening/closing companies and changing the situation is much more likely to trigger an investigation and they can go back 6 years if they want (I believe it's 6 in extreme cases, could be wrong). Having two companies open, dormant ones etc is much more likely to have them coming for a look to see why. Just do what your business needs. Don't start up contrived situations to try fix it. That will surely bring them sniffing. One of the points they look for when sniffing out aggressive tax avoidance are changes that are not required by the business and exist for tax favourable purposes which most of what you have said is.