There are ways of doing this without a tax liability but one of them isn't what the employer is proposing. The HMRC fact-sheet here explains more.
http://www.hmrc.gov.u...hildcarefactsheet.htm
It is the employer's look-out - technically it shouldn't be paying this out of petty cash since it is a taxable perk when done in this way. But the onus is on the employer to log it on the P11D as such, and to pay the additional NI and tax due calculated on the amount of £192.