Hopefully, the HSE won't come back at you with some awkward questions! If you're involved in tree-felling or supervising same, appropriate training is required. This is very dangerous work, and an area where HSE interest may be readily piqued. No mention of foot-spikes in various AFAG guides (e.g. AFAG 401), and with good reason I believe. My policy is never ask HSE for advice.

A HSE report from 2004 www.hse.gov.uk/agriculture/pdf/wahreport.pdf also mentions climbing irons; it also makes reference to “A Guide to Good Climbing Practice (GTGCP)”, so perhaps getting hold of a copy of that may be of some help? see http://www.trees.org.uk/...o-Good-Climbing-Practice

Thanks for everybodies input and as the question noted; I was just looking for opinions as there is no hard and fast situation/set of opinions/in depth guidance and after working in such areas since the 60's I am reasonably up to date but the situation I am addressing at this moment in time is where a new, and powerful, budget controller does not want to pay for such kit irrespective of opinions by very competent people who have used such kit in the correct circumstances for many years so any arguement put forward to allow purchase of such kit for particular situations needs to be a strong one

You could also have a look at the NPTC assessment schedule for a certificate of competence in tree climbing - http://www.nptc.org.uk/assessment-schedules/ - one of the assessment activities is to demonstrate knowledge of the effects on the tree of using climbing irons (spikes) - this suggests that the use of climbing irons should be restricted to dismantling of the tree or for aerial rescue.