Interest paid on late payment of sales tax is it allowable as expense if yes then why?

Late payment fees is of teo type one is penalty in nature and other is compensatry in nature, as per I.T.Act fine which is of compensatory in nature is allowed deduction penalty is not allowed.

not allowed as a deduction..

Google it. You will find numerous case laws on the subject where it was categorically held that interest on delay payment of sales tax is an allowable expenses

that what is my doubt many say allow and many say not allowed

when judicial precedents are there then why are you listening to contrary answers

Agreed, judicial precedents are enough for you to defend your position.

okay thank you

Income Tax act disallows any expense which is in the nature of a penalty which is imposed for any offence under any law or for doing something which is prohibited under any law.

Keeping this in mind, it can be concluded that delayed payment of sales tax is neither an offence nor it is prohibited under any law.
Therefore interest on such delayed payment will be an allowable expense.