The Gitzos all seem to be about £500. Am advised that Giotto would do an equivalent quality on a lot cheaper. Wonder if true?
Not true. Giottos make very good budget and mid-range tripods, but nothing really in the Gitzo class. As mentioned earlier, the only alternatives I've tried that can really compete with Gitzo Systematic are the high end Benros and Feisols (though there are no doubt others I've not used).
And as a comment, I wouldn't get too hung up on the centre-column thing. A quality tripod with the centre-column down is no worse than one without. Sure when pulled up you risk losing a lot of stability, but the option is at least there and sometimes you need it. Not perhaps for landscapes, but I use a centre-column for finer height adjustments in the studio when adjusting the legs is just such a PITA. Rarely take it up more than two or three inches though.
If you're used to a M'frotto 190, higher end tripods are just in a different league - as you might expect for the size and price. MF 190 is a great little tripod, but too short for most people without the CC pulled up quite a long way.
The other thing is the head, especially if you're thinking of spending a few hundred quid. A chain is only as strong as etc, and the head is the bit that you actually work with and move, the main user interface. Don't skimp on that.
Edit: as Jacob says below, Gitzo Systematics can be fitted with a choice of optional/detachable centre columns. The ultimate solution - for a price.