I don't disagree with how difficult it is compete with people who dont have to charge as much or any VAT. When DH was self employed, he often lost jobs to people who weren't VAT registered because they were cheaper for the customer.
But it doesn't change the fact that VAT is paid by your customers and not you.
Based on a 10% pre-tax net profit on a £1000 invoice:
Cost of sales (supplies, salaries) is £500 (gross profit of 50%)
Out of that gross profit you pay your overheads.(utlitities, loan interest, equipment repair etc) costing £350, leaving you with a pre-tax net profit of £150 out of which you pay tax and capital loan repayments.
Your turnover for that job is £1000, but at 20% VAT registered you charge the customer £1200 - the extra £200 is never yours - it's earmarked straight away for HMRC.
For the purposes of corporation tax only the £1000 is taken into account, not the £200.
I remember finding VAT payments really hard because when you are running a business on a hand to mouth basis, it's naturally tempting and often necessary to use the VAT money to pay day to day costs upfront, so when it comes time to pay the VAT I know it can feel really painful.
But the difficulties of competing against people who are not VAT registered and running a high turnover low margin business doesn't change the fact that VAT is calculated based on turnover but is not counted as part of turnover.
If you have been including the VAT on your invoices as part of your turnover calculations for corporation tax or double counting it in your VAT return (e.g. in the example above you calculated £240 VAT based on the total £1200 pound invoice instead of £200 on the ex-VAT £1000 portion) then it may be worth seeking some advice because you would be due a fairly significant rebate.