I'm trying to fit a new light switch (2-way, controlling 2 lights). There
are 2x common 2x L1 and 2x L2 connectors on the new switch.

I wired it yesterday and wired it identically to the old switch (which had
the same connector labellings). However, the downstairs light now comes on
when the switch is in the "OFF" position, and turns off when it's in the
"ON" position - and no the switch isn't upside down.

What can I do to remedy this?

TIA

Ian