We are arriving UK on 29th Apr and visa expires on 30th Apr. Our return date is 10th MAY. Will they allow us entry ? Is the expiry date like enter UK before 30th Apr or Expires on that day ?
My answer (which I simply deleted) was completely wrong. Let's try with a source, now :)
Once you’ve applied you can stay in the UK until you’ve been given a decision, as long as you applied before your last visa expired.
So: if your last visa expired and you didn't yet apply for a visa extension you can not stay.
What is the latest date that I can arrive in the UK with my visa?
The expiry date will be shown on the visa, but remember that this is also the last day on which you are permitted to stay in the UK.
Please note that upon the expiry of your visa, you are required to leave the UK.