Uk women mainly - help!

So I started a new job yesterday and this morning I found out I was almost 6 weeks pregnant. I am over the moon about being pregnant but am so annoyed about the timing of it with getting this new job I've been looking for a new job since May so was made up when I was offered this one. It's only an office job so no physical problems with being pregnant but I just want some advice on when should I tell my employer and if anyone is a boss or has dealt with this. How people reacted. Don't want them thinking I'm messing them around- I had done tests previous days before the interview and after and had negative results as my levels didn't double quick enough. PLEASE HELP ME !!