On a vat invoice do i duduct tax from labour charge before i add on the vat?

Work out the Vat on the TOTAL invoice value, THEN deduct the tax on labour.
So, for example...
Labour = 拢100
Materials = 拢60
Total = 拢160
+ Vat of 拢160 x 17.5% = 拢28
Total Invoice = 拢188
Minus tax on labour (18% I believe) 拢100 x 18% = 拢18
So amount to pay = 拢170

No the whole invoice is to include value added tax VAT

do you mean, do you charge vat on labour services ,the answer is Yes,

another words , every invoice you issue for goods or parts and labour, you would need to charge vat

I take it as you mean with regards to subcontractors (cis). I got the following from HMRC website:
ECH14225 - Construction Industry Scheme: CIS - General - Value Added Tax (VAT)
Where payment is made to a subcontractor who is subject to VAT and the subcontractor is

uncertificated
unmatched or
registered for payment under deduction
the amount from which the deduction is made is the payment excluding VAT.

Where a payment made to the subcontractor includes an element representing the cost of materials, the amount which may be excluded from the payment before deduction is made is the cost of materials before the VAT is added.

Where a payment is made to a subcontractor who is subject to VAT and the subcontractor is

certificated or
registered for gross payment
the gross payment amount shown on any CIS voucher or monthly return (CIS300) should be the amount due before VAT is added.

If following the CIOs enquiries and checks, VAT evasion is suspected the CIO should

discuss the matter with the CI Team Leader who will contact the local Indirect Taxes officer if appropriate.

Hope this helps

No you set your price and show that as the net amount, then add 17.5% vat onto that and total it.