Variable FTTP speeds

I've had FTTP for about six months - 300/50 with BT.

Over the past two months I've seen quite a lot of variability with the speeds, some days rock solid 300 but other times down to 20 or 30 with the upload sometimes down to around 10.

It it just network load with other users or should I get it checked ?

You could complain to BT. This BT speed test can be used to record a speed test result. It works on FTTC, I have not tried on FTTP.

Are you testing using an cable? - You should have a speed guarantee with BT..