What happens next?

[#1]

I have set my account to have a maximum spend on extra data if needed...
This might sound daft, but will I still be able to connect if I use all my data or am I cut off for the rest of the month?

[#2]

Yeah PJs right, once you hit your limit you will be limited and you pay £1 for every GB your over by!

[#3]

Not quite.
You can either elect to have a specific limit, have your speeds restricted if you hit that point, or alternatively go PAYG and have no such speed restrictions, but pay for additional usage.
What Sue has done is to set the data transfer watch, which when she reaches this amount, her speeds will be slowed down.

[#4]

do you not charge £1 for every GB when you hit that slowdown?

[#5]

Not if you're using the fixed rate product as opposed to PAYG.

[#6]

Ah right I never knew that!
You learn something new everyday 

[#7]

So when I hit my limit I get restricted to 128k/s....  Jeeez thats still bloody quick compared to the mobile phone connection I had... WIN WIN all the way.
I've been living with a very unsteady 3.5k/s for about 6 months and have never had better than 56k till now.... I'm buzzin!!!