Rail ticket combinations

[cjn]

I'm travelling from London to Ipswich soon, going out at peak time (midweek, about 5pm) and back the same day. I have a y-p railcard and per trainline.com the return fare is £31.80, however it's far cheaper to get two tickets as follows:

London - Chelmsford £7.60 (Std. Day Rtn)
Chelmsford - Ipswich £7.25 (Chp. Day Rtn)

I also hold a London monthly travelcard for zones 1-4 so I instead of buying a Liverpool St - Chelmsford ticket I want to get a Chadwell Heath (station in zone 4) - Chelmsford one, which is cheaper. Is this permissible?

I ask because I tried a similar thing on a trip to Reading (i.e. zone 4 to Reading ticket) and was told that I could only use the local Thames Trains, not the Great Westerns.

[isasmurf]

A saver return with a YPR is £18.15.

I also hold a London monthly travelcard for zones 1-4 so I instead of buying a Liverpool St - Chelmsford ticket I want to get a Chadwell Heath (station in zone 4) - Chelmsford one, which is cheaper. Is this permissible?I think you can do this. If travelling away from London you could have got a ticket from Boundary Zone 4, but AIUI these cannot be issued for travel into London.

I ask because I tried a similar thing on a trip to Reading (i.e. zone 4 to Reading ticket) and was told that I could only use the local Thames Trains, not the Great Westerns.
Was this a 1 day travelcard you used? These travelcards cannot be used in combination with other tickets on operators that do not call at stations within the travelcard area. I'm not sure about other types of travelcards though.