Thanks @Shallen. It's all to do with your own baby's routine. They say any slowing down of movements you should get checked.
I'm so used to mine being really active regularly throughout the day, and I feel her a lot when I go to bed and when I wake up.
We were with my family yesterday and out from about 12 until after seven. Usually if I'm busy in the day she's even more active at night because she moves less when I move around a lot, apparently the movement rocks them to sleep. But felt very little last night, had a bath, ate some chocolate, cold drink, lay on my side, felt a couple of movements and one strong kick but nothing close to what I normally expect.
Again this morning, I woke up and couldn't feel her. Ate some more chocolate (she likes it 
) had a cold drink and walked around and still nothing.
Rang maternity at about 9 and they asked me to go in at half ten. They can't monitor on machines until 28 weeks but she listened for around 5 minutes to her heartbeat and felt my stomach, took my temperature and blood pressure. Said she had no concerns and baby sounded healthy.
I've attached a pic of the sheet my midwife gave me about it. I asked today if the 'routine' she should be getting in to is daily or if I notice that she moves a lot one day and is quiet the next, that is a routine in itself. She said that at the moment she's small enough to move around so I can't always feel her movements but in the coming weeks I should be noticing she moves roughly the same amount each day.
Turns out today she'd gone and snuggled in right at the back on my pelvis which is why we suspect I couldn't feel her, she was well tucked in at the back but still moving around.