Any question answered...

It's a standard Assured Short-hold Tenancy break clause. Badly worded and with a misspelling, determine in stead of terminate (that I only noticed when I pasted it in my original post.)

Basically after the first four months I can give two months notice, whether it means six or seven months is moot as we've been there longer than both.

Or that's my understanding at least.

Sounds right.

The idea is it gives you an option to break at 6, but to do so you'd have to give notice at 4th, or at any point thereafter with the same notice i.e. 7th for 9th, 11th for 13th etc.