The easy way is if the gate is open which it has been for the last few weeks in fact the more i think about it the gate may even have been removed or you can get the bike past the stile at entrance closest to the Somme
Yip ...top of the Lead Mines.......learned to ride off road there as a nipper/teenager evry Sat/Sun and any other day I could get....know every trail like the back of my hand....enjoy....