UK mummies to be that are working???

Ok so I've been looking for a job for what feels like forever and with constant rejections I was getting a bit deflated. I have been offered an interview with a home care company meaning I'll be caring for the elderly within the community. My issue is I'm already nearly 19 weeks and will just be hitting 20 weeks at the interview - due to the nature of the job would I disclose I'm pregnant at the interview or would I best be leaving it till I've at least had the job offer??? I literally have no idea where to turn to for this information