You could drink it cold, although you might have problems completely dissolving the powder.
However, part of the psychological benfeit of Lemsip, is that curling up around a hot drink is supposed to be soothing and may help you to feel better.
You should find the same benefit from a mug of hot orange or blackcurrant and a couple of paracetamol
The hot drink helps with nasal congestion. If the powder had boiling water on it then left to stand until cold there would be the same benefits. The hot helps dissolve the sugar needed when you dont feel like eating when you have a bad cold. The cheaper versions as mentioned by scubadiver.
There are two kinds of Lemsip: One to dissolve in hot water & one in cold.
I expect the latter comes in handy if you are out & about & don't have access to hot water!
Thanks for all that. I actually emailed Lemsip and there answer is below.
It may help you to know that the use of hot water to mix the product is
based on the old cold and comforting remedy of hot honey and lemon drinks.
However, while there is no medical reason why the product may not be mixed
with cold water, it would take some time for the product to dissolve
properly in this way.
If you do not like the hot drinks, you may find Lemsip Max Direct a more
suitable alternative. This can be poured straight into the mouth and
swallowed. The Lemsip range also contains a number of products in a capsule
format which you may also wish to consider.