1) Contact baxi:http://www.baxi.co.uk/contact.htm
2) Which boiler wires? I don't know. Page 24 manual.
Manual says to disconnect link between terminals 1 and 2, and instert timer in-line.http://www.acwilgar.co.uk/Boiler-Manual-PDF/Baxi/Combi%20instant%2080E%20&%20105E.pdf
2) I can tell you about the timer wiring.
Timer is 230Volts
Not sure if you have British Hot-Neutral 230Volt, or Hot-Hot 230Volt.
Wiring is same 2 wires, but words to describe are different.
Let's say you have Hot-Neutral 230V
Connect Hot to L6
Connect Neutral to N5
This will power the timer so it runs and keeps time.
You can get Hot-Neutral wires from Hot-Neutral that arrive to power the boiler.
Now the timer terminals are separate.
E terminal is Earth or ground.
The Common is Hot wire.
The timer then turns on-off and switches back and forth between DHW and HTG.
HTG is heating
DHW is defrost.
Timer has 2 sets contacts.
When timer activates first set of contacts, then DHW defrost terminal receives power from Hot wire on Com terminal. At this time, all power is cut to HTG heating terminal.
When the defrost cycle ends, then the heating circuit receives power, and then the timer has programming that opens and closes a second set of contacts going to HTG heating terminal.
Which wires from boiler connect to each terminal, I am not sure.