It’s not legitimate.
Be warned about the latest text scam, seemingly offering you a tax rebate.
It’s very unlikely that it’s legitimate, as anything from the UK government, would have gov.uk at the end of it, and you’d probably get a letter. Most official texts are also set so that you are unable to respond.
Stay vigilant…. If it doesn’t look right, its probably not. Always phone the official helpline if you are unsure.