Re: £200 ?
If you want something remotely controllable, you'd pay a similar price for, say, the Hortsmann Z Wave thermostat (around 130-170, plus the cost of the actuator to switch the boiler; then add the cost of a separate Z-Wave controller if you wanted to provide remote access via the net).
You could do things cheaper if you opted for X10, though you'd still need to add a gateway for remote access; you could spend a lot more if you went for one of the GSM heating interfaces too.
If you're going all out for a full home automation system, then you might have a controller/gateway already, and can add a separate thermostat. But what you have here is all you need to do it, and for some people that's worth paying for (and, of course, if you do have a three wire connection, for a stat with a compensating heater, you can save £50 by not getting the RF version).
Yes, if you don't want the remote control, then it's a lot to spend. But if you do want that functionality, the price doesn't vary massively from some of the other ways of achieving this.