Jelly,
P001 clearly does apply to limited quantities of HCL. 4.1 requires all material to be properly packaged. P001 is the minimum standard for liquids.
4.1.1.5 (which you say applies) confirms outer packaging is required and in this case should be acid proof and have orientation marks.
" 4.1.1.5 Inner packagings shall be packed in an outer packaging in such a way that, under normal conditions of carriage, they cannot break, be punctured or leak their contents into the outer packaging.
Inner packagings containing liquids shall be packed with their closures upward and placed within outer packagings consistent with the orientation marks prescribed in 5.2.1.10.
Inner packagings that are liable to break or be punctured easily, such as those made of glass, porcelain or stoneware or of certain plastics materials, etc., shall be secured in outer packagings with suitable cushioning material.
Any leakage of the contents shall not substantially impair the protective properties of the cushioning material or of the
outer packaging."
Screening of goods for carriage of goods by air is basically predicated on correct declaration and marking of packages. Particuarly fo non-international freight as you do not know the routing so there is less of a a security risk and no smuggling.
Two inland routes that fly daily are Bournemouth-East Midlands and Exeter-London Stansted. Some is carried on passenger aircraft as well.
The lack of correct marking is resulting in more and more items being put on blanket bans by couriers regardless of their ADR, ICAO or IMDG status. An example is gas cylinders. Royal mail now have a ban on these even if they are empty.
And regardles of the ADR Royal mail have a TOTAL BAN on all Corrosives in the mail.
Corrosives (including aluminium chloride, caustic soda, corrosive cleaning fluid, dyes, acids, corrosive paint and rust removers, mercury and gallium metal)
- International – Not allowed in the mail
- UK – Not allowed in the mail
https://personal.help.royalmail.com/app/answers/detail/a_id/96/~/prohibited-and-restricted-items—advice-for-personal-customers