In whose name would the lease be? When you say split in half, is this a physical separation with each business having an individual lease agreement and separate utility supplies? Will Company A buy parts from Company B when carrying out repairs?
Did you tell her what you were considering and she agreed you coud do it, or did you tell her the basics and let her make suggestions? If the former, I would be very careful. Your accountant should challenge and test your ideas, not just agree to them.
Lease would be registered to Business A, it would be a physical seperation in the sense of a wall however it would all be one utility bill as I imagine that would massively complicate things? I made a mistake, company B would be carrying out repairs not A as A is already too close to the VAT limit. Company B will order in the new parts to carry out the mechanical work. I told her the exact plan and didn't let her assume anything. The whole time I must have gone back to the VAT situation atleast 5 different times and couldn't have made it more clear I only really want an accountant to assist in making sure everything I do in regards to avoiding VAT would be legal so I was a bit worried she ended up telling me what I wanted to hear to get my custom? I even at one point what would happen if HMRC disagreed with the accountants opinion and the response was "we will fight your corner". Wasn't really convinced, it seems an accountant can do as they wish and never be liable unless I've not understood it correctly.
You really need to speak to someone like @lesvatadvice but I believe that the above information could cause issues if endeavouring to separate the businesses and VAT office investigated
I am an online retailer with similar size of business little big in turnover and different products. I have an accountant who helps several other clients in the e-commerce business. contact me if you are still looking for it.
Since you are both self employed then company A is also you and company B is also your wife. If your wife/company B is accounting for the repair business but you/Company A do the actual repair work then it would look to me like artificial segregation