Seems to me two competing arguments;
1) Call the airfield to let them know you're transiting.
- Risk is you're heads-down switching frequencies, also you're no longer getting wider traffic info from LARS.
2) Stay with the LARS frequency.
- Risk is airfield traffic doesn't know you're transiting. Also you don't know any special airfield activity.
Which risk is higher? Very difficult to say.. especially in the case referred to with North Weald so close by.