The easiest way to get to the tunnel (they way we did as a kid). Go up the A47 Uppingham Road past Bushby and go up the hill. You'll see a large house on the left hand side called Winkerdale. There is a footpath to the right of this that goes though two fields, you get to the old bridge and turn right and follow the old track bed. If you follow for about 1/4 mile you will see the old aquaduct that is often leaking! When we lived there the old signal and railway workers shed was still there. A little after is the tunnel. You are best to get a decent torch. However I did ask a mate who lives in the area and he says the tunnel is often used by druggies and parties have been known to go on inside! Looking at the graffiti this could be the case. If you have the time you can clamber over the tunnel and a few fields and end up in Ingarsby. May parents lived in the old station house for a few months!. Plus if you go a bit further you can visit one of the most perfect deserted medieval village sites in the UK, plus the "Monks Grave", Mill ponds and old boundary roads. Have a good look at Google Earth and you can follow the old railway all the way to Marefield and beyond.
We are moving back to Leicester in July so this will be on my list of things to revisit so if you are up for a visit let me know!
Cheers. Always up for abit of exploring. Done Glenfield tunnel so another one around Leicester would be great.