Transferring Money Out Of Thailand - Another One..

I have the Foreign Exchange Cert from when I transferred a large sum into Thailand, at the time it was 70.8 bht to the £, I now want to transfer back to the UK, will I be allowed to convert the Thai baht received amount into £ equivalent (now about 35% more because of the weaker £), or only the same £ amount I brought in: ie bring in £100,000 would have equated to 7,080,000 bht, convert to £ at current rate = £137,465, will I be expected to pay witholding tax simply because of the exchange rate fluctuation?