One problem is that coming back on the Sunday there are buses, instead of trains, between Taunton and Bristol. Although there are through trains from Par to Paddington via Westbury, they are slightly slower and I am not sure that their calling points between Exeter and London have been fully programmed into the journey planners.
The offpeak return, which would cover the whole journey, would be £115.50 so the question is whether it is possible to beat that using Advances.
There is a £25 Advance for Huntingdon-Exeter St Davids on the following itinerary:
Huntingdon 0945
Kings X 1047
Paddington 1133
Exeter St Davids 1404
The train from Paddington continues beyond Exeter to Par and Penzance, and an Advance on the same train for Exeter-Par would be £16.50:
Exeter St Davids 1410
Par 1600
On the way back, you can get a Par-Huntingdon Advance for £63.50 on the following itinerary (later departures are more expensive):
Par 0915
Paddington 1504
Kings X 1623
Huntingdon 1722
The only way I could get that ticket was by starting with the National Rail Journey Planner for a single from Par to Huntingdon on 15 February departing at 0915 and in the Advanced options selecting: Avoid Taunton; go via London Paddington; and Avoid Basingstoke. When I clicked through to buy I was then being offered the desired ticket on the FGW website.
Total: £25 + £16.50 + £63.50 = £105 so only a £10.50 saving
Would coming back on the Monday be an option? If so, it might be worth looking for Par-Exeter and Exeter-Huntingdon prices for that day.
