This is an essential first step. If you don't own the land, then you must find out who does, and ensure that you have their permission to light a fire. Don't assume that "it will be ok" because all land is owned by somebody.
Never light fires on moorland, not even camping stoves or barbeques, the risk of a spreading fire is very high. Likewise, lighting a fire on peat can be massively dangerous, as the underlying peat can catch fire, and can start a fire which spreads underground. (Not sure if you can recognise peat? When you ask for permission, if the area is peaty, you will be told "No!")
It is also illegal to light a fire within 50 feet of the centre of a carriageway, that being defined as any way over which the public have right of way for the passage of vehicles: that means BOATs, RUPPs, and (to be safe) any track that looks as though vehicles have been along it.
