Trying to replace a DRAYTON standard Thermostat with a Programmable Honeywell T3 or T4 or similar

Stadders

I am trying to replace a DRAYTON standard Thermostat with a  Programmable  Honeywell T3 or T4 or similar.  The new ones all seem to be battery powered  The current one has the following connections  N - Blue, Live - Red,  3 - a yellow wire sleeved red and an obvious earth.
The honeywell has a  A B C With  I believe the A being the equivalent of the 3.  I believe it shows the Live (Sleeved red) going to the A and the other Live  (Real RED) going to the B.  Am I right in thinking that the Live (Sleeved red)  should go to the A and the other Real red should go to the B.  I believe I should then seal off the Blue.  I don't want to blow the device on fitting
.
Any ideas Please

Colsa100

For peace of mind an electrician should be able to do the job for less than £100.00 (£40 - £60) dependent on where you live.  Also your insurance company will be better to deal with if a qualified person does the job and there are any issues arising.
One main thing to point out is that you have the old red coloured wires (main red perhaps phase in and collared or sleeved red possible switch wire) and a new (2005) blue wire (possibly neutral?) A wiring diagram for the old Drayton would help.
Your T3 diagram shows the phase going to B with the switch wire on A. The T3 timer switch doesn't need a neutral but the boiler will.  An good qualified electrician will be happy to allay any doubt over what each wire is and where it goes as well as get the job done quickly without blowing up your boiler or setting fire to your house.

Stadders

The red and blue mix and a plain yellow are most disconcerting, I must say.  Not too keen on getting in a proper electrician for what should be a very simple job indeed.  I am working on the principle that the  lives are both in the circuit with the sleeved one only being live when the switch is activated by the thermostat.  Just looking at the circuit I am not sure it matters which red goes to A and which goes to B.  I was hoping that someone would confirm that for me.

Talldave

I think it's a standard three core and earth 6243Y cable in pre-2006 colours. It wouldn't be disconcerting to an electrician !
But as the thermostat is simply closing a relay, it doesn't matter which way around the live and switched live are connected. 

matelodave

I agree with Talldave but if you really want to be sure use a multimeter to check.- you could always download a diagram of the existing stat to confirm as well.
Older thermostats required a neutral so the heat anticipation heater would work, but this isn't required on a new thermostat - just make sure that you tape it up and tuck it away  securely and turn of the mains supply when doing the job