Tresspassing or not.

I am applying for planning permission on a site that my father owns. He got full planning permission 15 years ago but never built the house. He knocked a portion of his own front wall to gain access to the site.(as shown in the planning) the neighbouring landowner is the registered owner of the both sides of the road half way down in front of my dads wall. ( an anomaly my dad should own half the road the full lenght of his site) . He took my dad to court and the judge drew a line XY on the map and said we cannot tresspass north of the line. No order exists to the south and east. Since then the landowner has put down two large stones at the line XY.
When i applied for outline planning i clearly showed that we would knock more of my dads wall below XY to gain access. The landowner objected saying we are tresspassing. Is he corrrect or are we ok to proceed