Looks like here: -
https://maps.app.goo.gl/anVtvY2jKoiDVb6S6However Tollington Park is a long street and there are many streets leading rigt off it, so one could argue 'vague locus'. Certainly there are two NRT signs so one cannot argue inadequate signage, in my opinion.
There may be a 'technical' appeal argument, so wait a bit, but don't miss the discount deadline if that is what your father is minded to do.
Your mother as the owner, has legal responsibility for paying or appealing. Was your father following satnav ? Fatal in London nowadays, one must keep a very keen eye open for signs restricting entry to streets.
