I tihnk Heathrow is still supplies free bags (Glasgow did in August) - but you can just use a sealable freezer bag from your kitchen if you want to go the airport prepared (and pick up a couple of bags for future use!)
Uou can take up to 1000ml of liquids/make-up/toothpsate/nailvarnish but no one item can be more that 100ml. A bottle of nail varnish will be smaller than that - and so will most make up. Your "solid" make-up (eye shadow/pencils, powder blusher) does not count.
HTH. Have a lovely trip! ;)