The 1.2m 'rule' was superceded some time ago by, I believe, the
Construction (Health, Safety and Wefare) Regulations 1996. The 2m depth
rule (reg 6.3) in the latter has recently been superceded by the Work at
Height regulations 2005. The latter regs applies to not only working
above ground level but at ground level or beneath it. In short there are
no stipulated heights or depths - but there is a requirement to fully
consider falls etc within this framework.