The train takes about five hours (depending on the exact journey), and involves going in and out of London, with an Underground Journey as well. It isn't cheap - but is a lot quicker than the coach. There are shorter routes (changing at Birmingham) - but they would take longer than the fast trains in and out of London. Use the National Rail site for times and prices - you might get advance tickets and save some of the cost.
I doubt you will find a shorter way. National Express coaches take over 11 hours with one change. Flights from Glasgow can cost under £30, however, the trains take ages to get there from Windermere. You are best off setting an early alarm.
I would rather fly from Manchester at 0630 than travel from Cumbria to Stansted
As Christopher says. Book well ahead for specifically timed trains via
www.virgintrains.co.uk or a station ticket office
A railcard will save you a further 34% www.railcard.co.uk
Booking opens 11 weeks ahead of your journey
Do you like paying extra for your travel? Early departures are much cheaper - for a reason.
National express is best option
thanks to all.