Halifax - a little extra...information please

I saw a giant poster in the window of the Halifax today, offering 2.8% on a cash ISA.

Wow, I thought, great deal.

But on closer inspection it appears (in the small print, only visible if you get right up close to the window - unlike the 2.8% - I could see that from across the street) this rate is only for 12 months - they must just have accidentally missed that off the massive writing on the advert.
Then it is just 0.5%, which is the Halifax variable rate.

Still, I thought, 2.8% for 12 months is good.

Then I noticed in the small print it said 'variable' after the 2.8%. But even in the small print I couldn't see what or how or when it varied.

So I went in and asked an employee.
As an aside, he was nowhere near as smiley as the current crop of 'employees' on the Halifax adverts but mercifully he didn't sing.

After consulting the advert, the poster and the booklet (which I had already read) he was unable to tell me how, when or why the rate might vary. "To be honest, I don't know" were his exact words.
So I told him not to worry and told him I'd call the helpline on the leaflet.

After much button pushing, selecting of options and listening to long and carefully worded warnings I spoke to someone.

When I asked them about what varied they gave the impression that if the Bank of England change base rates then the Halifax would change the 2.8% too.
So I asked why it didn't state the difference anywhere, ie if base rates go up, or down, by say 0.2% so would the savings rate.

At this point they said it wasn't anything to do with the actual base rate,it is just a rate set by them.
So I said, "right now I think I get it, when the Bank of England change base rates, you can use that opportunity to change your rate as you see fit?"
"Well", she replied, "it doesn't have to be when the Bank of England change things".

"So let me get this straight" I said. You mentioned the Bank of England changing rates, but actually the 2.8% has nothing to do with the Bank of England base rate, and Halifax can simply change the 2.8% to any other rate at any other time.
"Yes"
"So why did you mention the Bank of England base rate? That confused me, it gave me the impression the reason for changing rates was driven by the Bank of England, not the Halifax"
I continued: "So this 2.8% is really only guaranteed for today only?
You could change it at any time, to anything the Halifax want to?"

"Yes"

Hmmm - didn't say on the giant poster in the window...

The Halifax advertising tagline is 'a little extra help'
Perhaps 'a little extra information' on the adverts would be better...