Thinking of buying our council house.

We were very lucky long time ago to get a council property to rent, we have moved from a 1 bed flat to a 2 bed house. We could really do with a 3 bed after we have had our 2 child, we have a boy and a girl. With the current council rules they can share a room till our oldest is X age, before they can offer us a bigger place. But to honest we don't want to move, we are happy with what we have, we are in a good school area, and my oldest is doing so well at her school we don't want to move. We would also like our youngest to have the same.
We are thinking of buy our current place off the council, in the near future. Then covering it into a 3 bed, as the 2 bedrooms are very large and could easily be done. This seems to be the only way we will get on the property ladder in our area what we can afford without pushing ourselves to hard. I have been reading about the discount you earn for being tenant for X period of time.

This is taking from the right to buy website:
You must have been a public sector tenant for at least 3 years in order to qualify for the Right to Buy. If you live in a house, you can get a discount of 35 per cent after 3 years tenancy. You also get 35 per cent after 4 and 5 years tenancy. For each extra year after that, you get another 1 per cent for each year of tenancy up to a maximum of 70 per cent. If you live in a flat, you can get a discount of 50 per cent after 3 years as a tenant. You also get 50 per cent after 4 and 5 years tenancy. For each extra year after that, you get another 2 per cent for each year of tenancy, up to a maximum of 70 per cent.

I was perviously told you had to live in the current home for at least 5 years before you can apply to buy said property. But i now read the above as you only need to be a council tenant for 3 years before being able to buy the property we have been council tenants for 9 years now, but only 2 of those have been in house. Can anyone confirm this?