On their website, London Midland give this service update:
"Due to the overhead wires having been brought down at Hanslope Junction, there are currently no trains running between Northampton and Milton Keynes, or on the direct Rugby to Milton Keynes route."
"As a result, services on the Euston line will be disrupted all day. Trains can run between Northampton, Rugby and Birmingham New Street but as most services normally come from London, delays and cancellations are likely on this route too. We are extremely sorry if your journey is affected."
London Midland tickets can be used on the following services for no extra charge:
East Midlands Trains between Wellingborough-London St Pancras
Chiltern Railways between Birmingham Moor St-London Marylebone