Hi folks, I'll get straight to the point.
A lot of the songs that I write (be it full songs or even just a riff or collection of riffs) sound a lot like other songs, (usually songs written by my favourite bands) usually without me realising it.

Needless to say I want my songs to sound like my own songs. It is a bit of a dent to my confidence in my songwriting abilities, although I have written my share of decent songs that sound original in the past.

How do I get past this? Has anybody else experienced this? How did you get past this?

For every action, there is an equal and opposite criticism.
There's always going to be a little of that, and you shouldn't worry too much about it. Honestly though, there's no real way to be overly proactive about avoiding something that you don't know that you are doing. When you realize it, decide if it's too close, and consider that different drums/vocals/etc change the sound A LOT. If it's still too close for your comfort, just change that part a little - you can probably keep the "structure" of it intact while changing the notes in a few places, and you shouldn't lose any quality for doing so.
1. Don't worry. That's totally normal.
I even think most of your favorite artists (un)consciously copy riffs/songs from their idols.

2. If it really bugs you, try taking those riffs to a different time signature. That's always a safe option... Just throw 2 dices and make a song with whatever combination you get (like 5/4 or 3/4).
Thanks for your help guys! I'm currently writing with a new band and a lot of my ideas are said to sound like The Darkness. Don't get me wrong, I love The Darkness, but I don't want to BE The Darkness.
For every action, there is an equal and opposite criticism.
if you're directly copying riffs than it's a problem, if it sounds like the song just vaguely (say the structure, verse, verse 2 chorus verse some breakdown (not the generic idea of breakdowns please) then fast again, use wah wah on breakdown, is the same as the song of your idol) then it's just fine, even more than fine, it's called being influenced and most possibly it'll be you who'll know that you got the song out of that song you heard and got influenced. it's totally totally normal
A lot of times when I write music I try to imitate the techniques and styles of my favorite bands. I think everyone does that so it's okay!
How old are you and how long have you been playing?

Honestly, being highly derivative is a pretty normal stage of creative development. If you're youngish, or you haven't been playing for that long, there's a good chance you'll become more original just as you continue to improve as a musician and get exposed to more musical ideas.
I'm 19. I've been writing songs since I was about 17 (I've been writing as long as I've been playing but I've never finished something until I was 17) but I've been playing since I was 13. This is the first time I've wrote for a band on my own so I'm really very self-concious of what (and who) my songs sound like.
For every action, there is an equal and opposite criticism.
It's cryptomnesia, and it can only go away by writing more. That's really all the advice I can give, write as much as you can. Just stop if it feels forced.

I still haven't completely gotten rid of it, I don't think anyone can.
Lol, that happens to me constantly and it's the most annoying thing in the world! My advice would be write some songs in weird scales so that you can't copy them. Really though, everything's already been written. That's the problem
Unless you go totally out of the norm like thrash bongo doom or something it will sound like something else....it has all been done before.....just do it better than they did....
I haz gotten gud