Why NI Number in SDLT form?

[AK]

I recently completed a property purchase and was asked for my National Insurance number by my solicitor to fill in an SDLT form. some questions:

1) Why do I have to give my NI number? is it
compulsory?

2) Why only the purchaser's NI no is asked for
on form and not the sellers?

3) Can the IR use my NI number in future to see
how many properties I own or sell?

4) If above is true how will IR ever know if
they dont ask for seller's NI no also?

Thanks in advance

[King_Maker]

1. 'Cos HMRC require it. Yes.

2. 'Cos it's the purchaser who Self Assesses SDLT.

3. Possibly - it is used to link your Tax records.

4. SDLT does not involve the seller.