I think back in the days of spectrum games any cheats required you to use a POKE. This was a way to "stop the tape" after the first set of wiggle lines. Then change various lines of codes then complete the load. As with all programming of the time extremely time consuming and normally a waste of time. But there does seem to be a few cheats around on the web but I cant see most of them as our firewall blocks 'Games' sites. Try here
if target=_blank>http://www.spynets.com/cheats/details.php?ID=2927<
br>
if
not a quick search for "manic miner cheats" on google should do the trick