How will plans to criminalise trespass affect hillwalkers?

Trespass is currently defined in law as a civil matter, but the government is consulting on making it a criminal offence. What’s the background on this proposed change of legislation?

There was a letter signed by about 30 Conservative MPs in 2010 proposing the criminalisation of trespass. [The gist of it] was that councils are complaining about groups of travellers moving into an area where previously they had rights,