Not normal, but common on these plants. If its not been planted more than a year or two and you live in a drier part of the country, or you've had no real rain for some time, it could need deep watering. Alternatively, if you live in a wet area and your soil is heavy and its been in the ground for longer than 3 years, then compacted soil causing poor drainage could be an issue.

Yellowing of leaves may also be caused by nutrient deficiencies, so a general purpose feed might be a good idea, if the other two possibilities mentioned above are not applicable - preferably a good one with trace elements such as Vitax Q4.

Difficult to pinpoint the cause because you haven't said what part of the country you're in, nor how long this plant has been in the ground.

Ok thanks for that, i live in Worcestershire and the plant is in the ground aprox 4 weeks, planted with pot so i can move it for the winter

It may,, then, need repotting, but its not a great idea to bury a pot in the soil - any plants within often push roots through the bottom or over the top of the pot and root into the surrounding soil within a few months anyway. Drainage in the pot may also be compromised, or the soil within the pot may be dry when the surrounding soil is damp. Do you know precisely which palm that is? If its a Trachycarpus, they're hardy in the UK and can be planted straight into the ground.

This is a washingtonia robusta, they told me to plant the pot in the ground ?

Well I don't agree with that advice - there are drawbacks, which I mentioned in my first answer. This palm, once mature, may be hardy down to -8 degrees C for short periods, but leaf damage may occur at those sorts of temperatures. Keep it in a pot by all means, but stand the pot out of the soil somewhere, potting on as it grows, and once its larger and more mature, risk planting it in the ground. Protect with fleece during cold winters, once its in the ground, although, if you live in a particularly cold part of the UK, or we have a very cold winter, that may not be enough protection to keep it alive. If you live in a mild part of the UK (the south west, for instance) then I'd risk planting it in the ground now.