What do mean by 'current'?
To keep a current aircraft rating then, for twins, you need a proficiency check within every 12 months (not 13 - that's pre-JAA). For singles you need to do something every 2 years - either fly 12 hrs plus some other bits, or fly a proficiency check. To keep an IR current, again you need a proficiency check every 12 months. You can do any of these checks any time in the final 3 months and they revalidate from your old expiry date. You also need to think about a current medical - evey 12 months or 6 months if you're over 40 yrs.
If you do nothing at all then you still have a valid licence - you just can't use it!