Hello, I'm new here - from France

Hello - I'm British but living in France.  I've just noticed some reddish brown eggs on my onions and shallots!  Never seen them before.  Very small, like butterfly eggs but glossy.  In groups of about 10 to 20.  Anyone any ideas what they might be?

Sounds like you'll have onion root flies hatching any day. Better get them all squashed ASAP. This is borrowed from No Dig Gardening:

Onion fly: These are not only onion pests, they also attack all members of the allium family, such as leeks, garlic and ornamental alliums.

Onion fly lay eggs which hatch into maggots and eat into onion seedlings usually between the leaves and small bulbs or roots. In older onions the onion fly maggots eat away at the bottom of the onion bulbs.

These onion pests will eventually cause the onion leaves to go pale, wilt then die off, the bulb, or at least the inside of it to become rotten and stinky and the plant to keel over and die.

The onion fly looks similar to a small house fly and can be found flying around early summer as it lays its eggs in seedlings or the soil at the base of plants.

After 3 days the eggs hatch and the larvae tunnel into the onion, where they dine non-stop for 3 weeks growing into full-sized 8mm long reddish brown maggots.

Fat and happy they burrow back into the soil and pupate, emerging as a new generation of flies 17 days later.

At the end of summer after a few generations, the final pupae over-winter until next spring.