Hello bubs! Please don't take any notice of just one poster, as we all answer in diferent ways.
Now, you have given us the right information in mentioning the habitat - woods. So, as you will know a Blue Tit well enough, my guess will be the more common Willow Tit. It's very similar in colouring (cream and black) to the Marsh Tit and both are found in woodlands, despite the latter's name. If you heard the call or song you would be able to identify it instantly. The Marsh Tit sounds like it's sneezing , with a bright 'pit choo' sound, while the Willow Tit wheezes with a zi zi call or a tyoo, tyoo song.