They didn't say "the law allows leggings" your twisting things again Chopper, er crossref.
They said the law does not allow leggings, however following concerns from parents and coaches about child welfare the RFU (and AFAIK only the RFU) allow leggings for certain age grades of rugby.
Ah, no, Phil, I am afraid you are mis-remembering
The RFU's official Newsletter Touchline DID confirm that leggings were permissible under the regualtions.
It stated that
[LAWS]:
'BASE LAYER REGULATIONS
Following enquiries from coaches and parents, the RFU can confirm that it is permissible under RFU Regulations for young players, up to Under 18s, to wear base layer stockings or tights in cold weather, in accordance with IRB Regulation 12.
This regulation states particular thicknesses. However, parents can assume that most common brands will comply, although players are permitted to wear them subject to the assessment of the match referee that the items are safe and pose no risk of injury to the wearer or other participants.''''
[/LAWS]
Regualtion 12 doesn't of course mention leggings.
Robbie added this commentary in the WIKI
This is contrary to the Law 4, and Law Clarification No. 5 of 2006 which defines underwear, but be aware, Whilst this new RFU ruling has published in Touchline, it has not yet made it to the RFU Regulations, so the authority of it isn't entirely clear.
There has been no change in the Laws or regulations since then