Right, on the outward journey, a £19 fare is available if you specify "via Manchester." This is a saving of £7 compared to the £26 fare available on the direct [17:36] train (although an excellent value £36.50 First Class fare is also available on this train, where you would be provided with a full Evening Meal service).
The direct train takes 2h 35m and gets you into London for [20:11]; going via Manchester takes 3h 41m and gets you into London for [22:33] (you would leave Lancaster at [18:52]). You would have to consider whether it is worth this inconvinience to save £7.
Before I continue any further, I would also point out that Virgin are having a "First Class Seat Sale" starting this Wednesday, with Lancaster to London costing just £28. You might want to wait until Wednesday to see if these cheap tickets are available on the [17:36] departure. I know it's not saving you any money, but you would get a First Class upgrade for just £2.
I am unable to find any cheap tickets on the return journey (Virgin seem to have pulled almost all Standard Class Advance tickets on that date), although again, it may be worth waiting for the First Class Seat Sale.