It is certainly possible - but whether it is practical is another matter.

The issue is obviously that he is a sole trader, so the VAT registration applies to him, and therefore to both businesses (rather than companies, strictly speaking). (I am assuming that when you say "he started a consultancy company" it is still him on a sole trader basis, and that he hasn't in fact started a limited company - if he has, then surely it would have to be registered separately for VAT.)

If you treat each business as a separate company in Sage, you'll have two VAT returns that you need to combine into one for submission to HMRC. (For all I know Sage might offer a means to do that - but it's not something I've ever had to do.)

You might be better off using using a single company in Sage, and setting the two businesses up within it as separate departments - and with some separate nominal accounts for each as necessary for the type of things that go through the business. (And certainly, if he has separate bank accounts for the two businesses, use a different bank account in Sage for each one). The big advantage of this is that you just have one VAT return, and can submit it directly from within Sage.

"he wants to be able to see how much he spends on different things, and also where the income is coming from and it is difficult to see that when it is all lumped under one nominal code"

And so he should. For a single business, as you've obviously already realised, that's straightforward enough with Sage (or any other package) - we get that information by assigning the income or expenditure by its nature; sales, material purchases, printing and stationery, etc.

What using departments adds - and why I suggested it - is you can then see how much has been received and spent on all those different things, according to which department you are looking at.

"So is there an easy way to go about it?"

I don't have Sage in front of me (wrong computer system) and I can't remember what you do to set it up - so this is going to be vague and may be inaccurate. Someone else will hopefully come along and correct me and/or fill in the blanks.

You probably need to go to something like the Tools menu, and choose Configuration; there's probably a tab on there for departments. Set department 1 to be the farm, and department 2 to be the consultancy.

After that, you input everything for both businesses as you do now for the farm, but you choose the department number depending on which business it relates to. (It should be a column in all of the inputting screens - and if it isn't, right click on the headings and it should be a column you can add)

So, for example, if he has stationery printed for the farm, it'll go to code 75somethingsomething, department 1 - but if he has stationery printed for the consultancy, it goes to nominal code 75somethingsomething, department 2. Inputting is as simple as that.

Getting the information out should be a case of finding the relevant reports for what you want and which allow you to specify departments - there should be such reports for things like P&L.

What I thoroughly recommend doing is simply going into practice mode in Sage, and just trying it. Set up a couple of departments, and put some typical transactions through for both businesses to get a feel for it, and look at the available reports.

"What happens to the information that has been entered in the 'old' way, would I have to delete that and enter all afresh in the 'new' sage and just go from April 2016 on wards"

That's too specific a thing for anyone to answer. It depends on what he wants you to do, versus what exactly is in that nominal account and the amount of effort involved, versus your abilities.

"Also I'm not sure how to do an opening balance that is not 0.00 and it is overdrawn balance."

I don't understand the question, I'm afraid.