I tried to register to that site but no e-mail as yet.
Just a few things i can think of at the moment.
I suspect, that due to permission already been given in 1985. you may have hit a stumbling block. The best way to stop this, would be to find a 'point of law'.
You'll need to go through all the paper work from previous applications.
If anyone could go through archives of the church and land, area, deeds, titles, etc., to see if there's a covenant or other documents which prohibits building on the land.
People to get in touch with:
Cadw.
"Cadw is the historic environment service of the Welsh Assembly Government. 'Cadw' (pronounced cad-oo) is a Welsh word meaning 'to keep'."
"We aim to protect the historic environment of Wales by working with partners and private owners."
http://www.cadw.wales.gov.uk/Prince Charles (for all, some people don't like him) he does keep banging on about protecting your heritage. Get a letter off to him, (recorded delivery) you might get his support or he might put you in touch with the 'correct people' to help.
Write to and try to get as many celebrities behind the campaign as possible, Tom Jones, Griff Reece Jones, Huw Edwards etc., You'll also get more media coverage this way.
I don't know if the welsh local elections are due, but if they are, get someone to stand as the "St Johns Church, Llantrisant Road Heritage Party" or something like that
and get people to vote with their feet to show the council you mean business.
Regards
Rewcastle