Heljan have done 20, 25 26 31 leaving 21,22,23,27,28,29 of which 23 is planned by DJM, 27 is v similar to 26 and 30 v similar to 31. That narrows the choice to 21,22,24,28,29
22 is a possible Dapol growbag job and not Eastern region so unless combined with a 21 (complex) that is out too, the probables are thus 21, 24, 28. The Eastern connection says 21, preservation connection says 28.