G-EMMA,
Track crawling is not something that your student X has to worry about.
Overall when one looks at the chart one can see that the aircraft was within a few nm of the planned track at all times. Thus navigation even on the unplanned diversion was quite accurate.
However, what I see as a whole is that the planning of the flight is poor in relation to airspace and in some cases, it is luck that has prevented an infringement.
I say that because;
a) Look at theose nice blue lines within the Andrewsfield ATZ. I do not know what manoeuvering was done but it does not look like a standard circuit pattern but more importantly, the ATZ boundary, the CTR boundary and the flight track all meet at the same place. A puff more wind and a bit more drift in a turn and wham...an infringement.
b) The nice yellow line is on the good side of the planned track and had the flight drifted to the other side by the same amount it would have entered the zone.
Overall, I can't see why the flight did not proceed via the nicely positioned and easy to recognise Braintree VRP outbound and inbound. Especially on the way in since the planned track is very close to the zone boundary prior to entering the ATZ.
I realise that Wallingford was unplanned but having got there, and thus being faced with an unplanned leg back to base, a route via Chelmsford VRP and Braintree VRP would be easier, safer and very unlikely to result in an infringement.
Your instructor needs to teach you defensive navigation i.e. using a slightly longer route at times to keep you safe even if it adds 2 or 3nm onto the miles.
Regards,
DFC