Whoever thought up this idea must be a complete nimrod.
For non-kipper mates please see
The Online Slang Dictionary | "N" Words | Page 9
As in:
"Rafair 7654, Boston Centre, say aircraft type"
"Boston, Rafair 7654, Nimrod sir, I spell N-I-M-R-O-D"
"Tee hee tee hee" Sounds of controller rolling on floor laughing.
or
"Norfolk Tower this is Spamjet 56C, what's that thing ahead of us?"
"Spamjet 56C, they call it a NIMRAAAAAD"
"Tee hee heee heee" Sounds of first officer choking on his coffee and doughnut.
Please, please, please Mr Cameron can you save the MRA4 and maybe call it something else like Triton Mk1?