As a subcontractor working for a principal contractor can I reclaim vat on purchases such as diesel if vat registered? I only work for one principal contractor so other incomes.
If you're VAT registered, carrying on an otherwise taxable activity and can show you billed the principal contractor and in accordance with the RCT VAT rules such that you did not charge VAT on your invoice, then you still should have input credit entitlement.
Which would mean you're going to be in a refund position (you didn't charge any VAT on invoices you issued to your customers). Revenue may probably ask for detailed workings before issuing a refund, and they'll probably be slow about it, particularly if it's a first refund claim.
There are also some amounts of VAT that can never be claimed - see below:
What VAT can you not reclaim?
You cannot reclaim VAT on the following costs even if you are registered for VAT and make only taxable supplies:
food, drink or other personal services for yourself, your agents or employees. The exception being to the extent that they are part of a taxable supply of services
accommodation, other than qualifying accommodation in connection with attendance at a qualifying conference
food, drink, accommodation or other entertainment services, where it forms all or part of the cost of providing advertising services
entertainment
passenger motor vehicles, excluding qualifying vehicles or vehicles used as stock in trade
petrol, unless used as stock-in-trade
contract work involving the handing over of goods when such goods are themselves not deductible
Goods purchased by an accountable person that are subject to a margin scheme
Expenditure incurred on the acquisition or development of immovable property forming part of the assets of a business, where the goods are to be used for a non-business purpose.