One of the basic principles of the planning system is that anyone can apply for planning permission on any piece of land. For example, I could apply for permission to erect a scale replica of the Eiffel Tower in my next door neighbour's garden - and it's possible that I could be granted permission. However, I couldn't implement that permission without my neighbour's consent because he owns the land.
With that out of the way, there are three points arising from the OP's query.
1) If your lease on the land has seven or more years left to run, it would appear that the applicant did not serve the correct notice until Article 7 of the Town and Country Planning (General Development Procedure) Order 1995. This has led to a clear breach of your right to comment on an application in which you have a direct legal interest. You could, therefore, take the matter to the High Court for judicial review. Be aware that there is time limit on applying for judicial review (normally six weeks).
2) The local planning authority has failed in its duty to consult you on the planning application. Presumably its general policy is to erect a notice in the proximity of your site, advertise the application in the local newspaper and send out consultation letters. You may wish to ask the planning officer to provide documentary evidence to prove that this was done.
3) While JohnD and Thermo generally spend their time on DIYnot falling out over the merits of painting concrete fence posts, they're both quite correct in urging you to see a solicitor without delay. I suggest going to the Law Society website and seeking out a specialist in planning law rather than randomly choosing some bod from the Yellow Pages. As in all walks of life, there are solicitors who are worth their money, and those that aren't.
Best of luck.