I've just replaced my very old light switches - a dimmer switch which controls the lounge lights and a 2 way switch which does the lounge and landing. Dimmer works fine but the 2 way only works the landing light. Help - very confused woman trying to do this!

Are you certain that all the switches you installed were marked as 3 way switches, 3 screws not counting any green grounding screw.

Yep..

If something is switched from 2 locations it uses 2 3 way switches and will have 3 connections, is this what you have?
And you also have a second switch?
What color wires are on the switch?
If dimming, you will need a 3 way dimmer.

Ah. Just checked the dimmer and it says 1 way!

That will teach me to try to do it myself! Thanks fellas

You're fine, there are 2 wires that connect between 2 three ways, they are called "travelers" and are usually the same color, and will connect to the 2 silver/white screws, The dark screw of 1 switch will be for constant power, the other 3 way dark screw goes to the light.
Good Luck

Lovely. Thank you.