Take a look here and here for information on expenses that can be reimbursed to an employee tax free whilst working abroad for a UK employer.
I hope this helps but let me know if you have any further questions.
If you didn't receive a subsistence allowance, then you can make a claim using a maximum of the lunch, dinner (not if dinner was part of the accommodation costs paid by your employer), drinks and hotel to office rates. You should limit your claim to the lower of what you actually spent and the maximum rates and you may be asked by HMRC to provide receipts.
Did the accommodation costs cover the provision of any meals?
Can you tell me where you stayed when you were in China, in a hotel or an apartment or house rented by your employer? How far from your accommodation was the place you worked?
Without receipts you won't get a deduction at all I'm afraid.
It's highly unusual for an employer not to pay an allowance for subsistence to an employee or to reimburse an employee for subsistence costs whilst working abroad. Therefore, the HMRC rules when strictly applied don't allow for a claim to relief subsistence to be made by an employee who is not reimbursed for such costs by their employer. The HMRC view is that if no reimbursement is made, subsistence expenditure is not necessary. Subsistence does not cover buying food which is consumed in a company provided flat, though that would probably be covered if the costs were reimbursed by the employer. It normally covers travel subsisitence costs. If an employee was sent abroad for a longer period, say a year or two or longer, they would be unlikely to be reimbursed for subsistence by their employer as they would effectively be living abroad and probably close to their work. The subsistence allowance is really aimed at those working a considerable distance from home.
Having said all that, I have seen HMRC allow subsistence claims using receipts where they have not been reimbursed but I have no case law to back that up. It may be that the claims got through because the box on the Sa102 employment pages (17) of the tax return for such claims covers travel and subsistence.