Production companies are always in need people of all shapes and sizes. Whether you consider yourself ugly or pretty, whether old or young but not too young, you need to be over 18. Mind you if you look younger than 18 you'll find lots of companies begging for you. The reason? Quite simply down to money, you can save them the cost of a carers for a child actors.
When you find get the contracts it can mean a lot of waiting around, that's normal for actors, but you get paid for that. Also don't expect to meet any famous stars, its' very much upstairs and downstairs in this business.
You can expect to get paid a minimum of £85 a day and extra for supplying your own clothing or providing a filmed 'walk-on' routine. there is also overtime is paid at around £11-12 an hour.
For more information I have given a list of three typical agencies, of course there are many more if you hunt around. If you visit enough there will certainly be work for you. Many just don't know this work is around!