Re: There something wrong with plastic
a: a plastic bag is difficult to clean, therefore difficult to recycle and therefore often thrown away. On the right-side of the pond of course, our plastic milk containers are made from natural-colour HDPE, I believe, which is just about the most recyclable plastic around. Quick rinse, shove it in the recycling bin.
b: the fuel doesn't have to be fossil (other than the oil required to make the plastic)
c: the fuel doesn't have to be fossil to make the glass (though it often is I imagine)
d: around here, glass bottles are usually doorstep-delivered (shops rarely have glass), collected from a central location, often the bottling plant, which these days usually deals in both glass and plastic
e: no special trips are made to collect empties, either if delivered (empties are collected when fulls are delivered) or if Joe Bloggs is buying from the shop - he can take back the empties when he goes to buy more. Additional fuel used for transport is therefore minimal - most of the fuel goes in pushing the vehicle around.
f: washing a bottle doesn't use much fuel, though I couldn't put a specific figure on it, and again it needn't be fossil (though in practice water is often heated by gas)
g: HDPE bottles are rarely (yet?) made from purely recycled plastic; some amount of "virgin" plastic is always added as the plastic degrades
h: glass bottles can be re-used many times, but WRAP reckons glass only beats HDPE plastic bottles after 20 uses. One story I saw elsewhere says the average glass bottle in the UK is reused 25 times, while another said 13 times. But of course...
i: glass can be 100% recycled pretty much indefinitely, recycled glass is exactly as good as "new" glass - unlike recycled plastics - and recycling uses vastly less energy than making new glass. One thing the WRAP survey didn't seem to make clear was whether their "20 times" was for new glass or recycled. If the former, then it would be far lower for the latter.
I'm sure there's a proper discussion of it out there somewhere. Maybe I'll look for it later, but right now the kettle has boiled and I need to get some milk - from a glass bottle - into a mug for a cuppa