They were divided into two batches : examples built at BR 's Swindon works were numbered in the series D800 to D832 and from D866 to D870 , had a maximum tractive effort of 52,400 pounds force and are the British Rail Class 42 of this article . They were divided into two batches : those built at BR 's Swindon works were numbered in the series D800 to D832 and from D866 to D870 , had a maximum tractive effort of 52400 l and eventually became British Rail Class 42 .