I think there is some confusion here. I'll try and explain what's going on as I see it.
Firstly, when you state that
banks take deposits and lend them out
you are referring to the Intermediation of Loanable Funds (ILF) model of credit creation. This is mechanistically and materially false as a model of banking.
In reality, banks simply create deposit balances when they extend credit and remove deposit balances when these loans are repaid. There is no connection or requirement for loans to be funded from previous deposits. See this from the Bank of England: BoE Working Paper No. 761
Now, let's consider the effect of corporate bond purchases on the money supply. If a private sector corporation issues savings bonds to raise cash, you are purchasing a financial instrument (presumably in return for interest payments). It will be instructive to analyse precisely how this transaction occurs.
Let's assume you and this company hold deposit accounts at different commercial banks. When you inform the company that you wish to buy their bond for £1000, your bank and their bank will communicate. Your bank will debit your deposit account, lowering its value digitally by £1000. Your bank will simultaneously instruct the Bank of England to decrease its reserve balance held with it by £1000 and credit the reserve balance of the company's commercial bank by £1000. Once the company's bank's reserve account has been credited by the Bank of England, it can proceed to credit the company's deposit account with them by £1000. The net result is that you have £1000 less in deposits but they have £1000 MORE in deposits. You will then own the issued corporate bond contract issued by the company to you.
Nowhere in the above analysis does the aggregate level of deposits in the economy increase. It is just a re-distributional effect endogenous to the private sector.
Yes, you own a liquid financial asset which was created out of thin air by the company issuing it. But it is quite rightly not considered currency and part of the money supply because it can not be used to pay taxes liable to the Government and therefore it cannot be used to purchase goods and services in the economy (You could theoretically try and offer the bond in exchange for a good (say £1000 valued car) but how would you pay the VAT due on that purchase in £ Sterling?). It's possible for these financial assets to be accepted as payment of debt (which has no tax obligation associated with it) but all this would do is cancel out some loan asset-liability balances and leave the created deposit (net financial assets remains unchanged) but this is rare.
Similarly, buying shares in a publically traded company has no effect on the net money supply. You purchase a share from someone who already owns it, or directly from the company issuing it. Your deposit value is transferred (via commercial bank reserve accounts at the Bank of England) to the seller's deposit account and you now own the share. No currency creation has taken place. You may later sell your share for a larger amount than you purchased it. But this does not create new money. YOU end up with a larger deposit balance at the end of the buying and selling transactions, but someone else ends up with a lower deposit balance (in aggegate). It's ALWAYS only distributional.
There are TWO ways for the money supply to increase. Either the demand for net saving in the private sector increases, resulting in the Government's deficit (private sector surplus) increasing, or the demand for credit in the private sector increases, resulting in commercial banks creating more deposit balances out of thin air.
Note that only the former method (Government deficit spending) can increase the NET money supply of the private sector because they are the only entity that sits outside the private sector. When banks create credit financial assets, they must simultaneously create financial liabilities. The net is always zero. But the Government only ever increases net financial assets (in £) when it spends.
Finally, let's consider the issuance of Government bonds (UK Gilts or US Treasuries for instance). In a given year, the Government spends its budget to provision itself and make payments to public sector workers, state pensions, companies in exchange for goods and services, etc. It does this by instructing the Bank of England to credit the reserve accounts of the relevant commercial banks, who then proceed to credit the deposit accounts of the final beneficiaries. Tax is then returned to the Government in the reverse process.
At the end of the year (in this simple example), there is often some £ money left over in both the deposit accounts AND the reserve accounts because less tax was returned than was initially spent. I'm ignoring commercial bank credit for now as it makes no difference to this analysis. To provide a safe store of value and target a particular interest rate, the Bank of England offers Government bonds. The excess reserves held by the commercial banks at the BoE are used to buy these new Government bonds. This DOES have the effect of deleting some of the reserve account balances held at the BoE and so reducing "High powered money" (i.e. liabilities of the BoE). However, it has no impact on the level of deposit account balances held by individuals and firms at the commercial banks. The excess £ money left over in deposit accounts after the Government spending and tax process is complete REMAINS in the economy after Government bonds are issued.
The conclusion of the above paragraph is that the money supply available for spending on goods and services in the real economy has gone up as a result. This could lead to an increase in the price level but not definitely as it depends on multiple other factors (such as production, bank credit, spending behaviour, etc).