Selling our house and our buyer wants to ‘gift’ us some of the payment as a direct transfer

As per the title, we are selling our house via an estate agent but have stated negotiating directly with a buyer. She is offering significantly more than asking price (asking £235,000). Currently the offer is £242,000 + £5000 directly into our bank when we accept the offer.

Now for us to not disclose this to our estate agent would say us £50 in commission and the buyer £100 in stamp duty, but are we sitting on a legal land mine considering this?

Edit:

Thank you all for the advise. I think most people think we are trying to defraud (which we aren’t!). It’s a weird deal that’s been put to us, and we are being slightly blinded by the prospect of the money as it would be extremely useful to us.

The buyer offer is to show how serious she is about it before we reject our other buyers, however we are going to speak to our solicitors about this today, as we want to make the deal with her - but legally. I came here for advise on what to do next as I’m not legally minded at all, and on the face of it she is giving us a 5k gift.