FYI, Virgin Atlantic is "VS" not "VA". Not trying to be pedantic but it is an important clarification because VA is Virgin Australia and DL and Virgin Australia used to have a close relationship along with bag-interlining (including on separate tickets) but DL and VS dropped their partnership a while ago. Conversely, DL does have a tight partnership (including checking bags across separate tickets) with VS and conflating the two codes could cause confusion in the responses as from your thread title, I thought you were referring to Virgin Australia (VA) but upon reading your OP, could tell you were referring to Virgin Atlantic (VS).

To answer your question: yes, if these are separate tickets, DL can through check your bag to the LHR-DEL flight operated by VS. If on a separate ticket, have a paper printout of your LHR-DEL ticket and let the agent know you need to through check your bag across the second ticket. Verify yourself the bag tag actually shows DEL as the final and not LHR before the agent places the tag on the bag and puts it on the belt.