Inveigling an invoice

For my small business (which is fully taxable) I made a purchase from a local branch of a well-known chain store. The receipt I was given did not seem to contain much information so I asked the cashier whether it was possible to run off a VAT invoice. She said that such requests could be fulfilled only by head office and she took my details and said that a VAT invoice would follow in the post. Two months down the line nothing has yet turned up. Is this something that I should be concerned about?

The other thought that occurs to me — should I be faced with the same circumstances in future — is whether there is a legal obligation on the person from whom the purchase is physically made to provide a valid VAT invoice rather than simply referring the purchaser elsewhere for this.

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