The points raised above will come into focus shortly, for there was a small snag with Joffre's plans for 1915, one that closely affected the BEF. To increase his forces for these large attacks Joffre required the BEF to take on more of the French-held line, specifically by replacing the French IX and XX Corps north of Ypres with British formations so that one of these corps could join in the Artois attack and the other extend the French front north of the La Bassee canal - a position currently held by I Corps of Haig's army.
Back in January French had agreed, albeit unwillingly, to carry out this relief as soon as he was reinforced by the 1st Canadian Division and the regular 29th Division, both of which were expected in February. Joffre then changed his mind and proposed letting the British retain the front north of the La Bassee canal - and launch an attack from there and from Armentieres along the Lys river valley.
The French XX Corps could therefore stay where it was, but IX Corps, said Joffre, was 'absolutely indispensable' to his Artois attack and must be relieved. Deadlock yet again; French could either abandon his attack at Neuve Chapelle or relieve IX Corps- and Joffre wanted him to do both.
On 28 February Haig visited his neighbour, the Tenth Army commander, General de Maud'huy, hoping to complete their arrangements for joint support in the coming offensive. Haig was then informed that unless IX Corps was relieved and sent to him, General de Maud'huy would be unable to offer any support to the British attack going in on his left flank at Neuve Chapelle; the attack of the Tenth Army would be postponed.
'The net result of his information', Haig told Field Marshal French, 'is that our proposed offensive action must be considered an entirely independent operation.' On 7 March Joffre confirmed de Maud'huy's statement, but the BEF went ahead anyway. Three days later, on 10 March 1915, the First Army attacked the German line at Neuve Chapelle.
The Old Contemptibles Page 44