help please advice on how to access our land

[spallan49]

Hi,
I am very worried. My dad has some land to the rear of a terraced row with shared access through an archway. (Deeds have easements etc) There was a gate and we had a key. The gate has been changed to one without a key eg, you open it from the inside. It has been a few years since we have been in but under 12. What now? The other person is a solicitor and is obviously trying to nick our land. My dad isn't well , a protracted legal battle would be bad.
Dad thought there was a key and he could just drill the lock off and fit a new one and post the key through the letter box.Or maybe just totally take the shutter down and replace it?Obviously he has no problem stringing out a costly legal case, we don't have that luxury. What can we do. Please give me good news.