Not true. You can contribute up to 100% of your relevant earnings per year, with a limit of £60k. Your employer can't salary sacrifice an amount that would take you below minimum wage, but if you have a lump sum like the poster you can contribute as much of that as you want into a SIPP as long as the total contribution don't exceed 100% of relevant earnings plus any unused allowance from past 3 tax years.
@alchal, you may go a little over your relevant earnings (£33k unless you have any other qualifying income) if you contribute the £30k lump sum and start doing £120 a week in the same tax year, but it almost certainly won't be a problem because you can carry forward unused allowance from the past 3 tax years.
I would open a SIPP for your lump sum and if you have the possibility make regular transfers out into it from the people's pension. You'll automatically get 20% relief added to your lump sum SIPP contribution by the SIPP provider, so the £30k will turn into £37.5k. Look into it yourself but standard advice is to invest into a low cost global index tracker like Vanguard FTSE All World ETF.