High resolution MERLIN observations of a newly-discovered four-image gravitational lens system , B0128+437 , are presented .
The system was found after a careful re-analysis of the entire CLASS dataset .
The MERLIN observations resolve four components in a characteristic quadruple-image configuration ; the maximum image separation is 542 mas and the total flux density is 48 mJy at 5 GHz .
A best-fit lens model with a singular isothermal ellipsoid results in large errors in the image positions .
A significantly improved fit is obtained after the addition of a shear component , suggesting that the lensing system is more complex and may consist of multiple deflectors .
The integrated radio spectrum of the background source indicates that it is a GigaHertz-Peaked Spectrum ( GPS ) source .
It may therefore be possible to resolve structure within the radio images with deep VLBI observations and thus better constrain the lensing mass distribution .