Selling land in Dharan, Nepal

I'm no lawyer, so all I can do is give you my personal advice.
1. Nothing easy about this transaction. Prepare yourself for the long pull. To conclude this transaction from start to successful completion, allow yourself up to 12 months. Personally, I'd be wary of anyone who tries to convince you that it can be done in a shorter span of time.
2. To begin with, and to gain time, I would advise you to start the process by marketing the property  from England. To do that, you risk nothing by placing a good detailed ad for the sale of that property in one or more popular classified online websites, notably the well known www.hamrobazaar.com . In your "for sale ad" make sure you display 4-6 photos and provide prospective buyers with a thorough description of the property. Make arrangements with a local person you know and trust, who can start showing the property on your or your father's behalf in Dharan. For convenience sake, be sure to include his local/nepali cell phone number  in the classified ad so prospective buyers can contact him directly for on-site visits, answer queries, etc. and more, importantly refer - read forward - any offers to you in England.
3. This on-the-spot person will in fact be your broker, and you can make arrangements with him to give him a percentage but only to be paid to him, on successful completion - at the end of the process, when the deal has been concluded at the lawyers.
4. As I said, this whole process is going to require time, so get yourself mentally prepared for that.
So step one:  market the property and first get an offer to buy, from a prospective purchaser.
Step two:       If that offer is acceptable to you, and you are ready to move forward, obtained solid bank and other references on him to ensure the person is serious potential party. Try to find out if he has the cash or will have to borrow?   After that, there will be plenty of time to appoint a good nepali lawyer to process the transaction and complete the deal for you or your father in Nepal. He'll tell you how to proceed, what documents are needed etc.
Just one word of advice: If the nepali lawyer asks for a power of attorney, to act in your or your father's  absence from the country, don't give it to him. Keep full control.
When and only when this nepali lawyer is ready to exchange contracts to close the deal with the prospective buyer, should you or your father consider having to fly to Nepal. But there is no harm in your father giving you a power of attorney, that's ok, so you can represent him here, and you can act for him in Nepal.
This is only personal advice, not professional advice. And for now, hold on to your Land Certificate and do not give it to any third party.
What I would advise, however, is for you to just bounce off the above ideas with an ENGLISH lawyer, and just get his reaction. He won't be able to do the actual deal but he may have other suggestions for you, things which I may have overlooked.
Hope this information will be useful for you. Good luck!