Go for it, it's not too hard. It's the ride back that is the killer.
Although said in jest, there is a little more to add. It was back in the mid 80's and was working in the city and one of my colleagues got chatting about cycling. He was brought up in Catford and he made me jealous saying his school had "games" at Herne Hill track! Anyway we challenged each other to do the LTB. And we persuaded quite a group from the office to take part as well. The others all arranged to meet at the bandstand on the common. Now living where I do, in longfield, the trains Sunday mornings are poor, so I decided I would cycle in, picking up a colleague along the way in Bexley Village.
So a ride to Clapham, where we met the others and duly rode the event to Brighton sea front, taking about 8 hrs. One of the office colleagues had borrowed a bike on the day and at the finish, vowed he would never ride a bike again. The others headed for the train back to London.
Not me, I didn't want to spend hours in a train back to London and then faced with another journey out to Longfield, I started riding in the direction of Lews and Crowborough. It was at this point when I "bonked". Stopped at a pub and downed 2 pints of orange juice and some food, but I was done. Rang my wife to come and rescue me. Did ride a little further to Tunbridge Wells where I waited at the Pantiles and eventually got home.
But not put off, I rode the LTB for the next 3 years and did the full return journey each time, even riding up the notorious Exedown.
LTB - it's easy
Good Luck,
Keith