Delta interviews were held at gatwick early part of this week, you may be to late for this one, but contact details are:-
Mr j o donnell
Atlantic regional maintenance manager.
delta airlines.
north terminal
gatwick airport,
west sussex.
For further info, Northwest no longer employ just A&P's since klm took over the gatwick line maintenance operation as part of the klm / northwest alliance, they now operate under jar66.
Your best bet is American at Lhr, or try fls who handle the continental contract at lgw, hope this info is of use to you.