Right an executive decision was made and this is what I did.
1) Poured 500ml of Tesco Everyday Value Thin Bleach into a bucket.
2) Topped to bucket up with water from the hot tap up to the 10 ltr mark.
3) Got one of me silk plants out of me tank and swished it arounds for 10 minutes on me phone timer.
4) Poured the bleach solution away and rinsed the bucket out with fresh water from the hot tap.
5) Dried the bucket with a kitchen paper towel.
6) Filled the bucket with 10 litres of fresh water from the hot tap.
7) Give me silk plant a good rinsing for 5 minutes in the fresh water.
8) Poured the fresh water away and repeated 6 and 7 two more times.
9) Shook the silk plant dry after the third bucket of rinsing.
10) When I did me Sunday Water Change I rinsed me silk plant in the waste changed water.
I then replanted me cleaned silk plant. It looks nice and clean in brightens up me tank again.
I'll let members know if me Guppies have any adverse effect to me bleaching this way.
I only did one of me plants because I didn't want to go over the top and harm me Guppies.
If everything is ok I'll do the same procedure to another silk plant next Sunday water change.